Discover how your heart works, one beat at a time.
Join us on a journey through the heart’s anatomy and function. From the chambers and valves to its electrical system, this clear and accessible guide will help you understand the incredible mechanics behind every heartbeat.
Empowering you with the knowledge to better understand your heart and take charge of your health.
In this section, we take a closer look at the structure and function of the heart — from the four chambers that keep blood moving, to the vessels that carry oxygen throughout the body. Learn how blood flows through the heart in a precise sequence, and how the pericardium helps protect and support each beat. We also explain what your heartbeat tells us, including the normal “lub-dub” sounds and what changes in rhythm or tone might reveal about heart valve function.
The heart muscle, or myocardium, is a specialised type of muscle that forms the walls of the heart. It contracts and relaxes with every heartbeat to pump blood throughout the body.
Unlike other muscles, the heart works continuously, even during rest. It has its own electrical system that sends signals to trigger each beat. These signals begin in the heart’s natural pacemaker, the sinoatrial node.
The muscle is made of cells called cardiomyocytes, connected by structures that allow electrical messages to pass quickly between them. This helps the heart beat in a smooth and coordinated way.
There are two key functions:
Systolic function: when the heart contracts and pushes blood out.
Diastolic function: when the heart relaxes and fills with blood.
Both are vital for healthy circulation. Conditions like high blood pressure or heart muscle damage can affect how the heart works. Doctors often measure these functions to help diagnose and manage heart conditions.
The heart has four valves that make sure blood flows in the right direction with every heartbeat.
Tricuspid valve: Sits between the right atrium and right ventricle. It opens to let blood flow into the right ventricle, then closes to stop it from flowing backward.
Pulmonary valve: Located between the right ventricle and the pulmonary artery. It opens when the right ventricle pumps blood to the lungs and closes to prevent blood from returning to the heart.
Mitral valve: Also called the bicuspid valve, it lies between the left atrium and left ventricle. It opens to let blood fill the left ventricle and closes when the ventricle contracts.
Aortic valve: Found between the left ventricle and the aorta, the main artery of the body. It opens to send blood out to the body and closes to stop it from flowing back into the heart.
Each valve plays a vital role in keeping blood moving in the right direction. If a valve becomes narrowed or leaky, it can affect how well the heart works and may need further assessment or treatment.
The coronary arteries are blood vessels that supply the heart with oxygen and nutrients. These arteries are essential for the proper functioning of the heart, and any blockages or damage can lead to serious health problems.
There are two main coronary arteries: the left coronary artery and the right coronary artery.
The left coronary artery branches into two smaller arteries — the left anterior descending artery and the circumflex artery. These supply blood to the left side of the heart, including the left ventricle, which is responsible for pumping oxygen-rich blood to the rest of the body.
The left anterior descending artery (LAD) is the larger of the two branches and plays a critical role in heart function. It supplies blood to the front and side of the heart, especially the left ventricle.
The right coronary artery supplies blood to the right side of the heart, including the right ventricle, which sends blood to the lungs to receive oxygen.
The coronary arteries lie on the surface of the heart and are surrounded by a layer of fat and connective tissue called the epicardium.
Blockages in these arteries can lead to coronary artery disease (CAD), a common cause of heart attacks. CAD develops when plaque builds up inside the artery walls, causing them to narrow and limiting blood flow to the heart.
The human heart is a remarkable organ that works continuously to pump blood around the body, delivering oxygen and nutrients to every cell. A key part of this process is the heart’s conduction system.
This system is a network of specialised cells that create and coordinate the electrical signals that control the heartbeat. These signals ensure the heart contracts in a regular and efficient rhythm.
The process begins in the sinoatrial (SA) node, located in the upper right chamber of the heart called the right atrium. Known as the heart’s natural pacemaker, the SA node generates the electrical impulses that start each heartbeat.
These impulses travel to the atrioventricular (AV) node, located near the centre of the heart. The AV node delays the signal slightly, giving the atria time to contract and empty blood into the ventricles before they contract.
From the AV node, the signal travels down the bundle of His, which splits into the right and left branches for each ventricle. These branches lead into the Purkinje fibres, which spread across the ventricular walls and trigger a strong, coordinated contraction of the heart muscle.
The conduction system keeps the heart beating in a steady and organised way, making sure blood is pumped efficiently to the lungs and the rest of the body.
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The Four Chambers That Keep Blood Moving
The heart is made up of four chambers that work together to circulate blood efficiently through the lungs and the rest of the body. These chambers are divided into two sides: right and left, each with an upper and lower chamber.
The upper chambers are the right atrium and left atrium. They receive blood returning to the heart. The lower chambers are the right ventricle and left ventricle, which pump blood out of the heart.
The right atrium collects oxygen-poor blood from the body and passes it to the right ventricle, which sends it to the lungs for oxygen. The left atrium receives oxygen-rich blood from the lungs and transfers it to the left ventricle, which pumps it through the aorta to supply the entire body.
Each chamber has a specific role in the cycle of blood flow, and their coordinated activity ensures that the heart functions smoothly and effectively.
The Journey of Blood Step by Step
Blood flows through the heart in a precise sequence, allowing oxygen-poor blood to be sent to the lungs and oxygen-rich blood to be pumped to the rest of the body.
The process begins when oxygen-poor blood returns from the body and enters the right atrium. It then moves into the right ventricle, which pumps the blood through the pulmonary artery to the lungs. In the lungs, the blood picks up oxygen and releases carbon dioxide.
Oxygen-rich blood then returns to the heart via the pulmonary veins and enters the left atrium. From there, it flows into the left ventricle, which pumps it out through the aorta to supply the rest of the body with oxygen and nutrients.
This cycle of circulation repeats with every heartbeat, ensuring that every cell in the body receives what it needs to function properly. The coordination of valves, chambers, and muscle contraction is essential for maintaining efficient blood flow.
This cycle of circulation repeats with every heartbeat, ensuring that every cell in the body receives what it needs to function properly. The coordination of valves, chambers, and muscle contraction is essential for maintaining efficient blood flow.
The Protective Sac Around the Heart
The pericardium is a thin, double-layered sac that surrounds and protects the heart. While the heart muscle pumps continuously, the pericardium helps to anchor it in place and reduce friction during each beat.
It has two main layers:
Between these layers is pericardial fluid, which prevents friction as the heart moves. The pericardium also helps limit excessive movement, prevents overexpansion, and acts as a barrier against infection.
Sometimes, the pericardium can be affected by conditions such as:
Doctors may use tests like an echocardiogram, ECG, or chest scan to assess the pericardium and decide on treatment if needed.
What Your Heartbeat Tells Us
When a healthcare professional listens to your heart with a stethoscope, they are assessing the sounds made by your heart valves as they open and close. These sounds can provide important clues about how well your heart is functioning.
A normal heartbeat produces two main sounds, often described as “lub-dub.”
These sounds help healthcare professionals evaluate whether the valves are working properly. A clear, regular “lub-dub” usually indicates healthy valve function. Extra sounds or unusual rhythms can suggest changes in how blood is flowing through the heart.
One common example is a heart murmur, which is an additional whooshing or swishing sound. Murmurs can be harmless or may point to issues like valve narrowing (stenosis) or leaking (regurgitation).
If abnormal sounds are heard, further testing such as an echocardiogram may be recommended to examine the structure and function of the heart in more detail.
The heart has four valves – the mitral valve, tricuspid valve, aortic valve, and pulmonary valve – each with a crucial role in regulating blood flow through the heart. These valves are essential for maintaining healthy circulation and play a critical role in keeping the body functioning properly.Â
The left coronary artery divides into two branches that provide blood supply to the left side of the heart. These two branches are known as the left circumflex artery, which supplies blood to the side of the heart, and the left anterior descending artery, which supplies blood to the front part of the heart.
Similarly, the right coronary artery originates from the right side of the aorta and supplies blood to the right and bottom part of the heart.
The conduction system is a network of specialized cells in the heart that coordinates the electrical impulses that regulate the heartbeat. It includes the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, and Purkinje fibers. Normal sinus rhythm is the regular, coordinated electrical activity of the heart originating from the SA node, resulting in a consistent heart rate and rhythm.
The left and right bundles are part of the conduction system responsible for transmitting electrical impulses to the ventricles. The left bundle is located in the left ventricle and the right bundle is located in the right ventricle. The bundles help to ensure the synchronized contraction of the ventricles.
When first-line therapies for angina, such as beta blockers, calcium channel blockers, and nitrates, prove inadequate or are not well-tolerated, second-line therapies may be considered.
Perhexiline is a unique medication that enhances the heart's ability to utilize fatty acids for energy, reducing its reliance on oxygen and lowering oxygen demand. This action helps improve blood flow and alleviates chest pain in some patients with refractory angina.
Nicorandil is another second-line option with a dual mechanism of action. It opens potassium channels in smooth muscle cells, causing vasodilation and enhancing coronary blood flow. Additionally, nicorandil also stimulates nitric oxide release, further dilating blood vessels and reducing heart workload.
Trimetazidine is an anti-ischemic agent that improves cardiac efficiency by enhancing glucose metabolism and shifting the heart's energy production to a more oxygen-efficient process. As second-line therapies, these medications offer alternative approaches for managing angina in individuals who do not respond adequately to first-line treatments or those experiencing side effects from other medications.
Lipid-lowering therapies play a critical role in managing coronary artery disease (CAD), a condition characterized by the narrowing of blood vessels that supply the heart. Among the most commonly discussed and debated classes of medications are statins, which effectively reduce cholesterol levels and are widely prescribed to lower the risk of cardiovascular events. Alongside statins, other medications like ezetimibe, fibrates, and niacin are also utilized to target specific aspects of lipid metabolism, such as cholesterol absorption, triglyceride levels, and raising high-density lipoprotein (HDL) cholesterol. Additionally, the introduction of medications that inhibit PCSK9, an enzyme involved in cholesterol metabolism, has provided a promising new approach to further lower LDL cholesterol levels. These PCSK9 inhibitors, such as Repatha (evolocumab), have shown significant efficacy in reducing LDL cholesterol levels in patients with CAD, especially for those who may not respond well to traditional therapies.
Nitrates are widely used to treat angina and provide quick relief for chest pain. Commonly available in the form of sublingual sprays or tablets, patches, and long-acting tablets, nitrates work by dilating blood vessels, allowing for increased blood flow and reduced resistance. This dilation eases the heart's workload, leading to a decreased demand for oxygen and prompt alleviation of angina symptoms. Sublingual nitrates act rapidly and are often used to provide immediate relief during angina attacks, while patches and long-acting tablets are employed for preventive purposes. However, nitrates may cause side effects such as headaches, dizziness, and flushing, which usually subside over time.
Calcium channel blockers, including amlodipine, felodipine, cardizem (diltiazem), and verapamil, are commonly prescribed for the treatment of angina. These medications work by inhibiting the influx of calcium into the muscle cells of the heart and blood vessels, leading to their relaxation. As a result, blood vessels widen, promoting improved blood flow and reduced blood pressure. In the context of angina, this relaxation decreases the heart's workload, lowering the demand for oxygen and alleviating chest pain. Calcium channel blockers offer a valuable treatment option for individuals with angina, but it is essential to be aware of potential side effects, which may include headaches, dizziness, flushing, and ankle swelling.
Beta blockers, such as metoprolol, propranolol, atenolol, carvedilol, and bisoprolol, play a crucial role in treating angina. By blocking certain receptors in the heart, they effectively reduce heart rate and the force of contraction, thereby easing the heart's workload. This mechanism of action leads to a decreased demand for oxygen, making beta blockers highly effective in relieving chest pain associated with angina. As with any medication, it's important to consider potential side effects, including tiredness, worsened asthma, erectile dysfunction in some males, and more vivid dreams during sleep. Consult your healthcare provider to determine the suitability of beta blockers for managing your angina and overall heart health.
Anti-platelet medications play a crucial role in preventing blood clot formation, reducing the risk of serious cardiovascular events such as heart attacks and strokes. Among the widely used anti-platelet drugs are aspirin, clopidogrel, and ticagrelor.
Aspirin: This well-known medication inhibits platelet activation, making it less likely for platelets to stick together and form clots. Aspirin is commonly used for primary and secondary prevention of heart attacks and strokes.
Clopidogrel: As a potent anti-platelet agent, clopidogrel works by blocking specific receptors on platelets, preventing them from aggregating. It is often prescribed to patients with acute coronary syndrome, those undergoing stent procedures, and for some cases of peripheral arterial disease.
Ticagrelor: Ticagrelor is another effective anti-platelet drug that works by inhibiting platelet activation. It is used in acute coronary syndrome, often given alongside aspirin to reduce the risk of heart-related events.
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