Heart Revision Notes

The heart's muscular wall, primarily composed of cardiac muscle tissue, is thick and strong to enable powerful contractions that pump blood throughout the body. This muscle is thicker around the ventricles, especially the left ventricle, because it must generate enough force to send blood to the entire body.

The muscular wall's strength ensures efficient circulation and maintains blood pressure. For example, during exercise, the muscular wall contracts more forcefully to increase blood flow to muscles.

Damage to this muscle, such as during a heart attack, reduces the heart's pumping ability, demonstrating its critical role.

• Composed of cardiac muscle tissue.
• Thicker in ventricles than atria, especially left ventricle.
• Contracts to pump blood effectively.

The septum is a thick muscular wall that separates the left and right sides of the heart. This separation prevents oxygen-rich blood on the left side from mixing with oxygen-poor blood on the right side.

By keeping these blood flows separate, the septum ensures efficient oxygen delivery to the body and proper removal of carbon dioxide via the lungs.

A defect in the septum, such as a hole (septal defect), can cause mixing of blood, reducing oxygen supply to tissues.

• Separates left and right sides of the heart.
• Prevents mixing of oxygenated and deoxygenated blood.
• Essential for efficient circulation.

The heart has four chambers: two atria and two ventricles. The atria are the upper chambers that receive blood; the right atrium receives deoxygenated blood from the body, while the left atrium receives oxygenated blood from the lungs.

The ventricles are the lower chambers that pump blood out of the heart; the right ventricle sends blood to the lungs for oxygenation, and the left ventricle pumps oxygenated blood to the rest of the body.

The left ventricle has a thicker muscular wall than the right ventricle because it must pump blood at higher pressure over a longer distance.

• Right atrium receives deoxygenated blood from the body.
• Left atrium receives oxygenated blood from the lungs.
• Right ventricle pumps blood to lungs.
• Left ventricle pumps blood to body.
• Left ventricle wall thicker than right ventricle wall.

One-way valves are located between the atria and ventricles (atrioventricular valves) and between the ventricles and arteries (semilunar valves). Their function is to prevent blood from flowing backward during heart contractions.

For example, the tricuspid valve is between the right atrium and right ventricle, and the mitral valve is between the left atrium and left ventricle. The pulmonary valve and aortic valve are semilunar valves controlling blood flow out of the ventricles.

These valves open and close in response to pressure changes, ensuring efficient and directed blood flow through the heart chambers and into arteries.

• Atrioventricular valves between atria and ventricles.
• Semilunar valves between ventricles and arteries.
• Prevent backflow of blood.
• Operate based on pressure differences.

The coronary arteries branch off from the aorta and supply oxygen-rich blood directly to the heart muscle (myocardium). This supply is vital because the heart muscle requires a continuous oxygen and nutrient supply to function effectively.

Blockage of these arteries can lead to coronary heart disease, reducing oxygen supply and causing chest pain or heart attacks.

For example, during physical activity, the heart muscle's oxygen demand increases, and coronary arteries dilate to meet this demand.

• Branch from the aorta to supply heart muscle.
• Provide oxygen and nutrients to myocardium.
• Blockage can cause heart disease.
• Adjust blood flow according to heart activity.

The circulatory system is a closed network of blood vessels that transports blood throughout the body. The heart acts as a pump, pushing blood into vessels that distribute it to tissues and organs. Blood must flow in a specific direction to ensure efficient delivery of oxygen and nutrients and removal of waste products such as carbon dioxide.

• Blood moves in a continuous loop from the heart to the body and back.
• Directional flow is maintained by vessel structure and heart valves.

Arteries are blood vessels that carry blood away from the heart. Their walls are thick and elastic to withstand the high pressure generated by the heart's contractions. Most arteries carry oxygen-rich blood, supplying tissues with the oxygen and nutrients needed for cellular processes.

For example, the aorta is the largest artery, transporting oxygenated blood from the left ventricle to the rest of the body.

• Arteries transport blood away from the heart.
• They have thick, muscular walls to handle high pressure.
• Typically carry oxygen-rich blood (except pulmonary artery).

Veins carry blood back to the heart. Their walls are thinner and less muscular than arteries because the blood pressure is lower. Veins contain valves that prevent blood from flowing backward, ensuring it moves towards the heart. Most veins carry oxygen-poor blood, returning it to the heart to be re-oxygenated in the lungs.

For example, the vena cava is a large vein that returns deoxygenated blood from the body to the right atrium of the heart.

• Veins transport blood towards the heart.
• They have valves to prevent backflow.
• Typically carry oxygen-poor blood (except pulmonary vein).

In systemic circulation, arteries carry oxygen-rich blood from the heart to body tissues, and veins return oxygen-poor blood to the heart. However, in pulmonary circulation, this pattern reverses: the pulmonary artery carries oxygen-poor blood from the heart to the lungs, and the pulmonary vein carries oxygen-rich blood back to the heart.

This distinction is important to understand the full pathway of blood flow and oxygen exchange.

• Systemic arteries carry oxygen-rich blood.
• Systemic veins carry oxygen-poor blood.
• Pulmonary artery carries oxygen-poor blood to lungs.
• Pulmonary vein carries oxygen-rich blood to heart.

The heart's pumping action and the structure of blood vessels ensure blood flows in one direction. Arteries branch into smaller arterioles and then capillaries where exchange occurs. Blood then collects into venules and veins to return to the heart. Valves in veins and the heart prevent backflow, maintaining efficient circulation.

This directional flow is vital for sustaining life by continuously supplying oxygen and nutrients and removing wastes.

• Heart contractions generate pressure to push blood through arteries.
• Valves in veins prevent backward flow.
• Capillaries allow exchange between blood and tissues.

The heart generates electrical impulses that trigger muscle contractions, enabling it to pump blood effectively. An electrocardiogram (ECG) is a device that detects and records these electrical signals using electrodes placed on the skin.

The ECG trace shows characteristic waves corresponding to different phases of the heartbeat: the P wave (atrial contraction), the QRS complex (ventricular contraction), and the T wave (ventricular relaxation). By analysing the timing and shape of these waves, doctors can assess the heart's rhythm and detect abnormalities such as arrhythmias or heart block.

For example, a regular ECG trace with consistent intervals between QRS complexes indicates a normal heart rhythm, while irregular spacing suggests an arrhythmia.

• ECG records electrical impulses generated by the heart muscle.
• P wave corresponds to atrial contraction; QRS complex to ventricular contraction; T wave to ventricular relaxation.
• ECG helps diagnose heart rhythm problems.

The pulse rate is the number of heartbeats per minute and can be measured by feeling the pulse at accessible arteries, such as the wrist or neck. Each pulse corresponds to a heartbeat that sends a pressure wave through the arteries.

To measure pulse rate, count the number of beats felt in 15 seconds and multiply by 4 to get beats per minute (bpm). For example, if 20 beats are counted in 15 seconds, the pulse rate is 20 × 4 = 80 bpm.

Pulse rate provides a simple, non-invasive way to monitor heart activity and can indicate changes due to exercise, stress, or health conditions. A normal resting pulse rate for adults typically ranges from 60 to 100 bpm.

• Pulse rate equals heartbeats per minute.
• Count beats for 15 seconds and multiply by 4 for bpm.
• Pulse rate varies with activity and health status.

The heart valves open and close to ensure blood flows in one direction. When valves close, they produce characteristic sounds that can be heard using a stethoscope placed on the chest.

The two main sounds are 'lub' (first heart sound) caused by closure of the atrioventricular valves (mitral and tricuspid), and 'dub' (second heart sound) caused by closure of the semilunar valves (aortic and pulmonary).

Listening to these sounds helps assess whether valves are functioning properly. Abnormal sounds, such as murmurs, may indicate valve leakage or narrowing, which can affect blood flow and heart efficiency.

• Valve closure produces heart sounds heard with a stethoscope.
• 'Lub' is closure of atrioventricular valves; 'dub' is closure of semilunar valves.
• Abnormal sounds can signal valve problems.

In clinical or school settings, pulse rate measurement is the simplest method requiring only a stopwatch and fingers to feel the pulse. It is useful for quick assessments before and after exercise.

ECG requires specialised equipment and electrodes but provides detailed information about heart electrical activity and rhythm.

Auscultation with a stethoscope is a common clinical skill to detect valve function and heart sounds. For example, a doctor may listen for a murmur indicating a faulty valve that needs further investigation.

• Pulse measurement: simple, quick, no equipment needed except stopwatch.
• ECG: detailed electrical recording, needs electrodes and machine.
• Auscultation: uses stethoscope to assess valve sounds and detect abnormalities.

The heart rate is the number of times the heart beats per minute (bpm). During physical activity, muscles require more oxygen and nutrients to sustain increased energy production. To meet this demand, the heart pumps blood faster by increasing its rate of contraction.

This increase in heart rate ensures that oxygen-rich blood reaches the muscles more quickly, and carbon dioxide and other metabolic wastes are removed efficiently. The nervous system detects increased muscle activity and signals the heart to beat faster through the release of adrenaline and stimulation of the sinoatrial node, the heart's natural pacemaker.

The intensity and duration of exercise influence how much the heart rate increases. For example, gentle walking causes a moderate increase, whereas running or cycling at high speed causes a much larger increase. After exercise, the heart rate gradually returns to resting levels as oxygen demand decreases.

• Heart rate increases to supply more oxygen during exercise.
• Adrenaline and nervous signals stimulate the heart to beat faster.
• Intensity and duration of activity affect the magnitude of heart rate increase.

To investigate how physical activity influences heart rate, students can measure their pulse rate at rest, during exercise, and after exercise. The investigation requires simple apparatus and careful control of variables to ensure reliable results.

Apparatus needed includes a stopwatch or timer, a method to measure pulse (such as using the radial artery at the wrist or carotid artery at the neck), and a safe space to perform physical activity like stepping or jogging on the spot.

The independent variable is the level of physical activity (rest, moderate exercise, vigorous exercise), and the dependent variable is the heart rate measured in beats per minute. Controlled variables include the duration of exercise, the method of pulse measurement, and environmental conditions such as temperature.

• Use stopwatch and pulse measurement at wrist or neck.
• Measure heart rate at rest, during, and after exercise.
• Control exercise duration and measurement method for consistency.

1. Sit quietly for 5 minutes and measure resting heart rate by counting pulse beats for 30 seconds and multiplying by 2 to get bpm.

2. Perform moderate physical activity (e.g., stepping up and down a step) for 3 minutes.

3. Immediately measure heart rate again using the same method as in step 1; record the bpm as the exercise heart rate.

• Count pulse beats for 30 seconds, multiply by 2 for bpm.
• Exercise for a fixed time to standardise intensity.
• Repeat measurements to improve reliability.

Record heart rate measurements in a table with columns for 'Condition' (rest, exercise, recovery), 'Pulse count (30 s)', and 'Heart rate (bpm)'.

Calculate the average heart rate from multiple repeats to reduce random error.

Plot a graph of heart rate against time or activity level to visualise changes. Typically, heart rate rises sharply during exercise and gradually decreases during recovery, illustrating the cardiovascular system's response to increased oxygen demand.

• Use tables to organise data clearly.
• Calculate averages from repeats for accuracy.
• Graph results to identify trends and patterns.

Ensure the physical activity chosen is safe and appropriate for the participant's fitness level to avoid injury or excessive strain.

Limitations include variability in pulse detection accuracy and differences in individual fitness affecting heart rate response.

Improvements include using a heart rate monitor for more precise measurements, standardising exercise intensity using a metronome or treadmill, and increasing the number of repeats or participants for more robust data.

• Choose safe, suitable exercise intensity.
• Be aware of measurement and individual variability.
• Use technology and standardisation to improve accuracy.

The heart is a muscular organ divided into four chambers: two upper chambers called atria (left and right) and two lower chambers called ventricles (left and right). The atria receive blood returning to the heart, while the ventricles pump blood out to the lungs or the rest of the body. The muscular walls of the ventricles are thicker than those of the atria, especially the left ventricle, which pumps blood at high pressure to the entire body.

The septum is a muscular wall that separates the left and right sides of the heart, preventing mixing of oxygen-rich and oxygen-poor blood.

• Four chambers: left atrium, right atrium, left ventricle, right ventricle
• Atria receive blood; ventricles pump blood out
• Left ventricle has the thickest muscular wall
• Septum separates left and right sides

The heart beats through a coordinated sequence of muscle contractions known as the cardiac cycle. First, the atrial muscles contract (atrial systole), pushing blood from the atria into the ventricles. This contraction increases pressure in the atria, opening the atrioventricular valves (tricuspid on the right, bicuspid or mitral on the left) to allow blood flow into the ventricles.

Next, the ventricular muscles contract (ventricular systole), which increases pressure inside the ventricles. This pressure closes the atrioventricular valves to prevent backflow into the atria and opens the semilunar valves (pulmonary valve on the right, aortic valve on the left). Blood is then forced out of the right ventricle into the pulmonary artery towards the lungs and out of the left ventricle into the aorta to supply the body.

After contraction, the muscles relax (diastole), allowing the chambers to fill with blood again, preparing for the next cycle.

• Atrial contraction pushes blood into ventricles
• Ventricular contraction pumps blood out to lungs and body
• Valves open and close in response to pressure changes
• Relaxation phase allows chambers to refill

Valves in the heart ensure blood flows in one direction and prevent backflow. The atrioventricular valves lie between the atria and ventricles. When atrial pressure rises during atrial contraction, these valves open to let blood flow into the ventricles. When ventricles contract, the increased pressure closes these valves, preventing blood from flowing back into the atria.

The semilunar valves are located at the exits of the ventricles. When ventricular pressure exceeds the pressure in the arteries, these valves open to allow blood to be ejected. When ventricular pressure falls after contraction, the valves close to stop blood from returning to the heart.

Valve function depends on pressure differences across them and the integrity of their structure, including chordae tendineae that anchor the atrioventricular valves to prevent inversion.

• Atrioventricular valves prevent backflow to atria
• Semilunar valves prevent backflow from arteries
• Valves open and close due to pressure changes
• Chordae tendineae support atrioventricular valves

Blood returning from the body enters the right atrium via the vena cava. Atrial contraction pushes this deoxygenated blood into the right ventricle. Ventricular contraction then sends blood through the pulmonary artery to the lungs for oxygenation.

Oxygenated blood returns from the lungs to the left atrium via the pulmonary veins. Atrial contraction moves this blood into the left ventricle. Ventricular contraction pumps oxygen-rich blood through the aorta to the rest of the body.

This continuous cycle ensures efficient circulation, delivering oxygen and nutrients while removing carbon dioxide and waste products.

• Right atrium receives deoxygenated blood from body
• Right ventricle pumps blood to lungs
• Left atrium receives oxygenated blood from lungs
• Left ventricle pumps blood to body

Consider a resting heart rate of 70 beats per minute. Each beat involves atrial contraction followed by ventricular contraction. The atria contract first, lasting about 0.1 seconds, pushing blood into the ventricles. Then the ventricles contract for about 0.3 seconds, pumping blood out. The remaining 0.4 seconds is relaxation, allowing chambers to fill.

If atrial contraction did not occur, ventricles would fill less efficiently, reducing cardiac output. Similarly, if valves failed to close properly, blood could flow backward, decreasing circulation efficiency and potentially causing heart murmurs.

This example illustrates how muscle contractions and valve function are essential for effective heart operation.

• Heart rate example: 70 beats per minute
• Atrial contraction precedes ventricular contraction
• Proper valve function prevents backflow
• Disruption reduces efficiency of blood circulation

The heart is a muscular organ responsible for pumping blood throughout the body. During physical activity, muscles require more oxygen and nutrients to produce energy. To meet this increased demand, the heart must pump blood faster, which causes an increase in heart rate (the number of heartbeats per minute).

• Heart pumps oxygenated blood to muscles.
• Increased muscle activity raises oxygen demand.
• Heart rate increases to supply more oxygen.

When exercise begins, receptors in muscles and joints detect movement and send signals to the brain. The brain responds by stimulating the sympathetic nervous system, which releases adrenaline (epinephrine). Adrenaline increases the rate and force of heart contractions, raising heart rate and cardiac output. This ensures more blood, carrying oxygen and glucose, reaches active muscles quickly.

• Movement detected by receptors triggers brain response.
• Sympathetic nervous system releases adrenaline.
• Adrenaline increases heart rate and contraction strength.

The increase in heart rate during physical activity depends on several factors:

Intensity of exercise: More intense activities require greater oxygen delivery, causing a higher heart rate.

Fitness level: Well-trained individuals have more efficient hearts and may have a lower increase in heart rate for the same activity compared to untrained individuals, as their stroke volume (blood pumped per beat) is higher, reducing the need for a very high heart rate.

• Higher exercise intensity → higher heart rate.
• Fitter individuals have lower heart rate increase due to efficient heart function.
• Stroke volume and heart rate together determine cardiac output.

Regular aerobic exercise strengthens the heart muscle, increasing stroke volume. As a result, the heart pumps more blood with each beat, allowing the resting heart rate to decrease. For example, a well-trained athlete may have a resting heart rate as low as 40 beats per minute, compared to the average 70–80 bpm in untrained individuals. This lower resting heart rate indicates improved cardiovascular efficiency and health.

• Exercise strengthens heart muscle.
• Stroke volume increases, pumping more blood per beat.
• Resting heart rate decreases with regular training.

Consider a person whose resting heart rate is 70 bpm. When jogging at moderate intensity, their heart rate might increase to 130 bpm to supply muscles with more oxygen. If the same person regularly jogs and improves fitness, their resting heart rate might drop to 60 bpm, and jogging heart rate might be 120 bpm for the same effort, showing improved cardiovascular efficiency.

• Resting heart rate: 70 bpm → 60 bpm after training.
• Jogging heart rate: 130 bpm → 120 bpm after training.
• Improved fitness reduces heart rate for same activity.

The coronary arteries are blood vessels that branch from the aorta and supply oxygen-rich blood directly to the heart muscle (myocardium). This supply is essential because the heart requires a continuous and abundant oxygen supply to maintain its pumping action.

When these arteries become narrowed or blocked, the flow of oxygenated blood to the heart muscle is reduced. This condition is known as coronary heart disease (CHD). The blockage is usually caused by the build-up of fatty deposits called plaques inside the artery walls, a process known as atherosclerosis.

Reduced blood flow causes the heart muscle to receive insufficient oxygen, especially during increased activity or stress. This can result in chest pain (angina) or, if a coronary artery becomes completely blocked, a heart attack (myocardial infarction), where part of the heart muscle is damaged or dies due to lack of oxygen.

• Coronary arteries supply oxygenated blood to heart muscle.
• Blockage reduces oxygen supply, impairing heart function.
• Complete blockage can cause heart attacks.

A diet high in saturated fats and cholesterol contributes to the formation of plaques in the coronary arteries. For example, regularly consuming fried foods, fatty meats, and processed snacks increases blood cholesterol levels, promoting atherosclerosis.

Physical inactivity worsens this effect by reducing the efficiency of the cardiovascular system and contributing to obesity, which is itself a risk factor. Regular exercise helps maintain healthy blood vessels and reduces cholesterol levels.

For instance, a person who eats a high-fat diet and leads a sedentary lifestyle is more likely to develop CHD than someone who eats a balanced diet and exercises regularly.

• High saturated fat intake increases plaque formation.
• Lack of exercise contributes to obesity and poor cardiovascular health.
• Balanced diet and regular exercise reduce CHD risk.

Chronic stress can increase blood pressure and heart rate, placing extra strain on the heart and arteries. Stress hormones may also contribute to the development of plaques.

Smoking introduces harmful chemicals like nicotine and carbon monoxide into the bloodstream. Nicotine causes blood vessels to constrict, reducing blood flow, while carbon monoxide reduces oxygen delivery by binding to haemoglobin.

For example, a smoker under constant stress has a compounded risk of developing CHD due to both vascular damage and reduced oxygen supply.

• Stress raises blood pressure and heart workload.
• Smoking narrows blood vessels and reduces oxygen transport.
• Combined effects accelerate coronary artery damage.

Genetic predisposition means some individuals inherit genes that increase their likelihood of developing CHD, such as those affecting cholesterol metabolism or blood pressure regulation.

Age is a significant risk factor because arteries tend to stiffen and accumulate plaques over time, making older adults more susceptible to CHD.

Gender also influences risk; men generally develop CHD earlier than women, possibly due to protective effects of female hormones before menopause. However, post-menopausal women’s risk increases and can approach that of men of similar age.

• Inherited genes can increase CHD susceptibility.
• Older age correlates with higher CHD risk.
• Men typically develop CHD earlier than women.

Coronary heart disease results from the blockage of coronary arteries, impairing oxygen supply to the heart muscle and potentially causing angina or heart attacks.

Multiple risk factors contribute to CHD, including modifiable lifestyle factors (diet, inactivity, stress, smoking) and non-modifiable factors (genetics, age, gender).

Understanding these factors helps target prevention strategies such as promoting healthy diets, encouraging physical activity, managing stress, and discouraging smoking, especially in individuals with genetic predisposition or advancing age.

• CHD is caused by blocked coronary arteries reducing oxygen supply.
• Risk factors include lifestyle and inherited or demographic factors.
• Prevention focuses on managing modifiable risks to reduce CHD incidence.

Diet influences the levels of cholesterol and other fats in the blood, which are critical factors in the development of coronary heart disease. Consuming high amounts of saturated fats and cholesterol can increase low-density lipoprotein (LDL) cholesterol in the bloodstream. Elevated LDL cholesterol contributes to the formation of fatty plaques inside coronary arteries, narrowing them and restricting blood flow to the heart muscle.

A diet rich in fruits, vegetables, whole grains, and lean proteins provides essential nutrients and fibre that help lower LDL cholesterol and maintain healthy blood vessels. Reducing intake of processed foods, trans fats, and excessive salt also helps control blood pressure, another risk factor for CHD.

For example, replacing butter (high in saturated fat) with olive oil (rich in unsaturated fats) can improve cholesterol profiles and reduce plaque formation risk.

• High saturated fat intake raises LDL cholesterol, increasing plaque buildup.
• Fibre from fruits and vegetables helps reduce cholesterol absorption.
• Excess sodium intake can raise blood pressure, stressing arteries.

Regular physical activity strengthens the heart muscle, improving its efficiency and increasing the volume of blood pumped per beat (stroke volume). Exercise also raises high-density lipoprotein (HDL) cholesterol, which helps remove LDL cholesterol from the bloodstream, reducing plaque formation.

Physical activity promotes better circulation and helps maintain a healthy body weight, lowering the strain on the heart and blood vessels. It also reduces blood pressure by improving arterial elasticity and reducing stress hormones.

For instance, brisk walking for 30 minutes daily can increase HDL cholesterol levels and lower resting blood pressure, contributing to a decreased risk of coronary artery blockage.

• Exercise raises HDL cholesterol, aiding cholesterol clearance.
• Improves heart efficiency and circulation.
• Helps control body weight and blood pressure.

Coronary heart disease results from atherosclerosis, where fatty plaques narrow coronary arteries. Diets high in saturated fats and cholesterol accelerate plaque formation by increasing LDL cholesterol levels. High blood pressure damages artery walls, making them more susceptible to plaque deposits.

Exercise counteracts these effects by improving lipid profiles and reducing blood pressure, slowing or preventing plaque development. Together, a healthy diet and regular exercise maintain arterial health and reduce the likelihood of blockages that can cause angina or heart attacks.

An example is a person who switches from a fast-food diet to a Mediterranean-style diet and incorporates cycling into their routine, which can significantly reduce their CHD risk over time.

• LDL cholesterol promotes plaque formation in arteries.
• High blood pressure damages artery walls, facilitating plaque buildup.
• Exercise and diet improve blood lipid levels and arterial health.

To reduce CHD risk, individuals should adopt a balanced diet low in saturated fats, cholesterol, and salt, and rich in fibre, vitamins, and minerals. Regular aerobic exercise, such as swimming, jogging, or cycling, for at least 150 minutes per week is recommended.

Avoiding smoking and managing stress complement diet and exercise in reducing CHD risk. Monitoring blood pressure and cholesterol levels helps assess the effectiveness of lifestyle changes.

For example, a person might plan weekly meal menus focusing on vegetables and lean meats and schedule daily walks to meet exercise goals, tracking progress with a fitness app.

• Choose foods low in saturated fat and salt, high in fibre.
• Engage in moderate aerobic exercise regularly.
• Monitor health indicators to guide lifestyle adjustments.