Heart explained

Your heart is a vital organ#

Your heart is a muscle that pumps blood to every part of your body. The blood it circulates delivers the oxygen and nutrients your body needs to function. The heart is about the size of a clenched fist and weighs between 300 and 450 g.

It sits in the middle of your chest, behind and slightly to the left of your breastbone.

If you are of average body weight and size, your body holds about five litres of blood, all of which passes through your heart roughly once a minute. When more is needed, such as during exercise, your heart can pump up to four times that amount each minute.

The four chambers of the heart#

Your heart has a right and a left side, separated by a wall called the septum. On each side there is a small collecting chamber called an atrium, which leads into a larger pumping chamber called a ventricle. In total there are four chambers:

• the left atrium and right atrium (the upper chambers)
• the left ventricle and right ventricle (the lower chambers)

The right side of your heart collects blood as it returns from the rest of your body. This blood is low in oxygen, so your heart pumps it to your lungs to pick up more oxygen.

Once it has taken on oxygen, the blood returns to the left side of your heart, which pumps it out to the whole body through a large artery called the aorta. Blood pressure is the force that this pumping blood exerts on the walls of the arteries.

Each atrium connects to its ventricle through a one-way valve. The valve on the right side is the tricuspid valve, and the valve on the left is the mitral valve.

The heartbeat#

The familiar ’lub-dub’ sound of the heartbeat comes from the rhythmic closing of the heart valves as blood is pumped in and out of the chambers.

The heart rate is regulated by a special cluster of cells in the right atrium called the sinus node. The sinus node prompts the upper chambers to contract first. It then sends an electrical impulse to a second cluster of cells, the atrioventricular node, which lies between the upper and lower chambers. This electrical impulse causes the lower chambers to contract.

At rest, your heart beats approximately 60 to 100 times a minute.

Blood vessels of the heart#

The main blood vessels of the heart include:

• Coronary arteries – like any other organ, the heart muscle needs its own oxygen supply. The coronary arteries sit on the surface of the heart and supply the heart muscle with blood.
• Aorta – the largest artery in the body. Oxygen-rich blood is pumped into the aorta from the left ventricle, and the aorta then divides into branches that carry blood all around the body.
• Pulmonary arteries – carry blood that is low in oxygen from the right ventricle to the lungs.
• Pulmonary veins – return oxygen-rich blood from the lungs to the left atrium.
• Venae cavae – two large veins that deliver blood low in oxygen to the right atrium. The superior vena cava carries blood from the head and upper body, while the inferior vena cava carries blood from the lower body.

Common heart conditions#

There are many different types of heart condition. ‘Heart disease’ is a broad term covering the various conditions that affect the heart. Some common ones include:

• Coronary heart disease – occurs when the coronary arteries supplying the heart muscle become narrowed or blocked by a build-up of fatty deposits (plaque). It can cause angina and heart attacks.
• Angina – chest pain caused by a build-up of plaque in the coronary arteries. Part of the heart muscle may not receive enough blood and oxygen, causing chest tightness, discomfort or pain. Pain or discomfort may also be felt in the arms, neck, jaw, shoulders or back.
• Heart attack – happens when something, usually a blood clot, cuts off the flow of blood to part of the heart. Without oxygen and nutrients, the affected heart muscle begins to die. A heart attack is not always fatal, especially if you receive immediate medical treatment, but it can still cause lasting damage to the heart.
• Abnormal heart rhythms (arrhythmias) – a range of conditions where a fault in the heart’s electrical system affects its pumping rhythm. Atrial fibrillation is the most common type, in which the heart beats irregularly and often fast.
• Heart valve disease – damage to the heart valves can make it harder for the heart to pump blood around the body.
• Congenital heart disease – problems with the heart or blood vessels that a person is born with. These can include blockage of blood flow, abnormal flow of blood within the heart, or a heart that has not developed properly.
• Heart inflammation – includes pericarditis (inflammation of the outer lining of the heart) and myocarditis (inflammation of the heart muscle).
• Rheumatic heart disease – damage to the heart valves that develops after acute rheumatic fever. It remains more common in some communities and in people who have lived in regions where the disease is widespread.

Symptoms of heart disease#

Different heart conditions can cause different symptoms. It is important to be aware of the following warning signs, which may indicate a medical emergency such as a heart attack:

• Chest discomfort or pain – this can feel like uncomfortable pressure, aching, numbness, squeezing, fullness or pain in your chest. It may spread to your arms, neck, jaw, shoulders or back, and it can last for several minutes or come and go.
• Sweating or a cold sweat
• Shortness of breath or difficulty breathing (with or without chest discomfort)
• A racing, pounding or fluttering heartbeat (palpitations)
• Light-headedness, dizziness or feeling faint
• Feeling anxious
• Nausea, indigestion or vomiting

If your symptoms last more than 10 minutes, are severe, or are getting worse, call your local emergency number (for example 911 in the US and Canada, 112 across the EU and many countries, 999 in the UK, or 000 in Australia) immediately for an ambulance. In an emergency, do not drive yourself to hospital.

Key points#

• The heart is a muscular pump that delivers oxygen and nutrients to the whole body through four chambers and a network of blood vessels.
• An electrical system, starting at the sinus node, sets the heart’s rhythm and causes the chambers to contract.
• Coronary heart disease can cause angina and heart attacks when the coronary arteries become narrowed or blocked.
• Different heart conditions can have different symptoms, and warning signs such as chest pain need urgent attention.
• Call for emergency help if chest discomfort lasts more than 10 minutes, is severe, or is getting worse.

Where to get help and trusted information#

For evidence-based global health guidance, see Source: World Health Organization (WHO).