The heart is the body’s muscular pump. It continuously circulates blood around the body, delivering oxygen and nutrients to every cell while removing carbon dioxide and waste products.
An average adult heart beats around 100,000 times each day, pumping approximately 7,000–8,000 litres of blood every 24 hours.
At rest, the heart pumps around 5 litres of blood per minute, but during vigorous exercise this can increase to 20–35 litres per minute, depending on fitness.
Despite weighing only around 250–350 grams, the heart supplies every organ in the body with the blood needed to survive.
The primary functions of the heart are to:
Location and Size
The heart is roughly the size of a clenched fist (approximately 12 cm long, 8 cm wide and 6 cm deep) and weighs around 250–350 grams.
It lies within the chest (thoracic cavity), between the lungs in an area called the mediastinum. About two-thirds of the heart sits slightly to the left of the breastbone.
Note: Although many people think the heart is entirely on the left side of the chest, most of it actually lies near the centre of the chest.
The bottom of the heart (the apex) points downwards and slightly to the left.
The heart is enclosed within a tough, double-layered sac called the pericardium, which contains a small amount of lubricating fluid that allows the heart to beat smoothly with minimal friction.
Internal Anatomy
Four Chambers: The heart consists of four chambers: the right atrium, right ventricle, left atrium and left ventricle.
Heart Valves: Four valves (tricuspid, pulmonary, mitral and aortic) ensure blood flows in one direction only.
Septum: A thick muscular wall separates the right and left sides of the heart, preventing oxygen-rich and oxygen-poor blood from mixing.
Coronary Arteries: These arteries branch from the aorta and supply oxygen-rich blood directly to the heart muscle itself.
The heart functions as two pumps working together.
The right side receives oxygen-poor blood returning from the body and pumps it to the lungs, where carbon dioxide is removed and oxygen is absorbed.
The left side receives oxygen-rich blood from the lungs and pumps it through the aorta to supply the entire body.
Each heartbeat has two main phases:
Diastole: The heart muscle relaxes, allowing the chambers to fill with blood.
Systole: The heart muscle contracts, pumping blood into the lungs and around the body.
The heartbeat is coordinated by the heart’s own electrical conduction system.
Sinoatrial (SA) Node: The heart’s natural pacemaker generates electrical impulses that begin each heartbeat.
Atrioventricular (AV) Node: Briefly delays the electrical signal before passing it to the ventricles, ensuring the atria empty before the ventricles contract.
Bundle of His and Purkinje Fibres: Carry the electrical impulse rapidly through the ventricles, producing a coordinated contraction.
Fascinating Heart Fact: The heart generates its own electrical impulses and will continue beating even if removed from the body for a short time, provided it receives oxygen and nutrients.
The heart does much more than simply pump blood.
Maintaining Blood Pressure: By adjusting its pumping force and heart rate, the heart helps maintain a healthy blood pressure.
Responding to Exercise: During physical activity, the heart increases both its rate and the amount of blood pumped with each beat to meet the body’s increased demand for oxygen.
Supporting Temperature Regulation: By increasing or decreasing blood flow to the skin, the heart helps regulate body temperature.
Hormone Production: The heart produces hormones called natriuretic peptides (including atrial natriuretic peptide, ANP), which help regulate blood pressure, salt balance and body fluid levels.
Working with Other Organs: The heart works closely with the lungs, kidneys and blood vessels to maintain oxygen delivery, fluid balance and normal circulation.
Ischaemic Heart Disease (IHD)
Ischaemic heart disease (IHD) occurs when fatty deposits (atherosclerosis) gradually narrow the coronary arteries, reducing blood flow to the heart muscle. It is one of the leading causes of death worldwide.
Heart Attack (Myocardial Infarction)
A heart attack occurs when a coronary artery becomes completely blocked, causing part of the heart muscle to lose its blood supply. Prompt treatment greatly improves the chances of recovery.
Chronic Heart Failure (CHF)
Heart failure occurs when the heart is unable to pump blood as effectively as the body needs. It does not mean the heart has stopped working.
Atrial Fibrillation (AF)
Atrial fibrillation is the most common sustained abnormal heart rhythm. It causes the upper chambers of the heart to beat irregularly and increases the risk of stroke.
High Blood Pressure (Hypertension)
High blood pressure makes the heart work harder and increases the risk of heart attack, stroke, heart failure and kidney disease if left untreated.
Doctors commonly assess heart health using:
Blood Pressure: Measures the force of blood against the walls of the arteries.
Electrocardiogram (ECG): Records the heart’s electrical activity and can detect abnormal heart rhythms or evidence of previous heart damage.
Echocardiogram: An ultrasound scan that shows the heart’s chambers, valves and pumping function.
Blood Tests: Troponin helps diagnose a heart attack, while cholesterol, glucose (or HbA1c) and lipid levels help assess cardiovascular risk.
B-type Natriuretic Peptide (BNP) or NT-proBNP: These blood tests measure hormones released when the heart is under strain. High levels may indicate heart failure and help doctors decide whether further investigation (such as an echocardiogram) is needed.
Exercise Stress Test: Assesses how the heart performs during physical activity and can identify reduced blood flow to the heart muscle.
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