Heart explained

The heart is nestled between the two lungs in the centre of the chest, behind the breastbone. Its functions are to pump oxygenated blood around the body, and to deliver deoxygenated blood and waste products (carbon dioxide) to the lungs.

The heart is shaped a little like an upside-down pear, is about the size of a clenched fist, and weighs between 300g and 450g. At rest, the heart pumps about four to five litres of blood every minute.

The heart operates automatically, but responds to 'information' received from other parts of the body by changing its output accordingly. For example, hard-working muscles need more oxygen, so the heart (and lungs) picks up the pace to supply the body's increased needs.

The four chambers of the heart
The heart is a double pump with four chambers, each separated by valves that only permit blood to flow in one direction. Basically, the right side of the heart pumps deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the body.

The two sides of the heart are separated by a muscular wall called the septum. The right upper chamber (atrium) takes in deoxygenated blood from the body and squeezes it into the right lower chamber (ventricle). From there, the blood is taken by an artery to the lungs, where the carbon dioxide is replaced with oxygen.

Oxygenated blood enters the heart's left upper chamber (atrium). It is then pumped into the lower left chamber (ventricle) and then into an artery (the aorta), where it starts its journey around the body again. Blood pressure refers to the amount of force the pumping blood exerts on arterial walls.

The heartbeat
Each atrium is connected to its ventricle by a one-way valve. The valve on the right side of the heart is called the tricuspid valve, while the valve on the left side is called the mitral valve.

The familiar 'lub-dub' sound of the heartbeat is caused by 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 situated in the right atrium, called the sinus node. This prompts the atria to contract first; then an electrical impulse is sent to a second node (the atrioventricular node), which is found between the atria and their ventricles. After a brief delay, the ventricles contract. On average, the adult heart beats around 70 to 80 times every minute.

The heart's blood vessels
The blood vessels of the heart include:

• Vena cavae - deoxygenated blood is delivered to the right atrium by two veins: one (superior vena cava) carries blood from the head and upper torso, while the other (inferior vena cava) carries blood from the lower body.
• Pulmonary arteries - deoxygenated blood is pumped by the right ventricle into the pulmonary arteries that link to the lungs.
• Pulmonary veins - the pulmonary veins return oxygenated blood from the lungs to the left atrium of the heart.
• Aorta - the largest artery of the body that runs the length of the trunk. Oxygenated blood is pumped into the aorta from the left ventricle. The aorta subdivides into various branches that deliver blood to the upper body, trunk and lower body.
• Coronary arteries - like any other organ or tissue, the heart needs oxygen. The coronary arteries that supply the heart are connected directly to the aorta, which ensures a rich supply of oxygenated blood.
• Coronary veins - deoxygenated blood from heart muscle is 'dumped' by coronary veins directly into the right atrium.

• Heart murmur - an audible vibration or humming heard through the stethoscope, caused by somewhat noisy blood flow within the heart. Faulty heart valves are a common cause, but usually the murmur does not indicate an abnormality.
• Heart valve disorders - for example, a faulty mitral valve allows blood to move backwards from the ventricle into the atrium. This condition is called mitral regurgitation.
• Coronary heart disease - fatty deposits or plaques build up inside one or more of the coronary arteries (atherosclerosis). This constant silting narrows the artery. Untreated, coronary heart disease can lead to angina or a heart attack.
• Angina - if the coronary arteries are narrowed, part of the heart muscle may not receive enough blood and oxygen. This causes the sensations of chest tightness and pain that are typical of angina.
• Heart attack - if a coronary artery is blocked, the heart is starved of oxygen and nutrients. Heart muscle cells (myocardial cells) are damaged, and may die without prompt treatment.
• Congenital disorders - the heart of a foetus may not develop properly. Problems include the blockage of blood flow inside the heart or blood vessels, abnormal flow of blood within the heart, or the heart itself may be underdeveloped.
• Pericarditis - inflammation or infection of the pericardium, which is the membrane surrounding the heart.

• Chest pain
• Tightness in the chest
• Shortness of breath
• Irregular heartbeat
• Unusually fast or slow heartbeat
• Lightheadedness
• Fatigue.

• Your doctor
• Cardiologist.

• The functions of the heart are to pump oxygenated blood around the body, and to deliver deoxygenated blood and waste products (carbon dioxide) to the lungs.
• The heart is a double pump consisting of four chambers, each separated by valves that only permit blood to flow in one direction.
• Disorders of the heart include coronary heart disease, angina, heart attack, valve diseases and congenital disorders.

This page has been produced in consultation with and approved by:


(Logo links to further information)