How The Heart Works

The Heart  |  The Coronary Arteries  |  Normal Heart Rhythm | Heart Terms Glossary

The Heart

The basic function of the heart is to pump blood, rich in oxygen and nutrients, through blood vessels called arteries to the body. The oxygen is used by the body's tissues, and the veins carry the blood, now low in oxygen, back to the heart. 

There are two sides to the heart, each of which acts as a separate pump. The two sides are further divided into two chambers, giving four chambers in total. The upper chambers, the atria, collect blood, and the lower chambers, the ventricles, contract to pump the blood out. 

The right side of the heart receives blood, low in oxygen, from the veins throughout the body and pumps this blood to the lungs to collect more oxygen. 

The left side of the heart receives blood, rich in oxygen, from the lungs and pumps this blood around the body, through arteries to the tissues in need of oxygen.

In order to reach all the different organs and muscles throughout the body, blood has to be pumped at high pressure. To do this, the heart has to be very strong. However, to keep it working hard all the time, the heart needs a very good blood supply and this is provided by the coronary arteries and their branches.

Find out about Normal heart rhythm

Coronary Arteries

The coronary arteries branch from the aorta (the main artery leaving the left side of the heart)  are the first  to receive the oxygen rich blood. There are two coronary arteries, the right and left, and they are relatively small, with each being only 3 - 4 mm in diameter.
The two coronary arteries pass over the surface of the heart, meeting at the back and almost forming a circle.

The left coronary artery has two main branches, called the anterior descending and the circumflex. These two branches then divide further into smaller  branches of their own. The left coronary artery and its branches supply most of the left ventricle. The left ventricle is the more muscular and larger of the two ventricles, as it has to do the hard work of pumping blood all around the body. The right coronary artery is usually smaller and supplies the right ventricle and the underside of the heart.
 
In coronary artery disease, the coronary arteries become narrowed and the heart muscle becomes starved of the blood and oxygen it needs. The process whereby the coronary arteries become narrowed is known as atherosclerosis.

Normal Heart Rhythm

The heart has its own specialised electrical system, which allows an impulse to travel through its muscles causing them to contract and pump the blood around the body. 

The electrical impulse is produced by a special part of the right atrium (the top chamber) called the sinus or sinoatrial (SA) node. This is frequently called the heart's natural "pacemaker". The electrical impulse travels through the muscle of the atriums causing them to contact and push the blood towards the ventricles, the lower chamber. 

The impulse then comes to the atrio-ventricular node or AV node. This acts like a junction box and the impulse is delayed momentarily before it enters the muscles of the ventricles through fibres which act like wires. This is known as the Purkinje system.  As the impulse travels along these fibres, the ventricles both contract,  pushing the blood out of the heart to the lungs and the body. 

In a normal heart beat, each impulse from the heart's pacemaker results in the atria and ventricles contracting regularly and in the correct sequence.   The heart beats between 60-100 beats per minute.

It is normal for our heart to sometimes beat faster or slower depending on our state of health,  if we are exercising or resting. Occasionally things go wrong with the electrical system of the heart.   This results in an irregular heartbeat is called an arrhythmia.