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The structure and function of the heart

Hadyn Luke posted this on Tuesday 14th of May 2013 Hadyn Luke 14/05/2013

Tags: Anatomy and physiology


Our blog on the structure and function of the heart will give a useful understanding of how the heart works for anyone thinking of following a health and fitness course.

Personal trainers and other fitness professionals will often monitor a client’s heart rate to measure how hard they are training – and how effectively. Incorporating cardio-vascular workouts into a fitness regime will strengthen the heart and help prevent heart disease.

What is the heart?

The heart is essentially a large muscle that pumps oxygen and nutrients around the body.

Located behind the sternum (breastbone), slightly to the left of centre, the heart is made up of three layers:

  • Epicardium – outer, protective layer
  • Myocardium – thick muscular walls
  • Endocardium – inner layer of tissue

It is held in place and protected by the pericardial sac. The two layers of the pericardium – the fibrous pericardium and the serous pericardium – work together to allow the heart to contract vigorously when needed, for example if a personal trainer is working with a client on a high-intensity, cardio-vascular gym programme. The layers of the pericardium also keep the heart from expanding too far and overfilling.

The functions of the left and right side of the heart

The right side of the heart pumps deoxygenated blood through to the lungs (systemic circulation). There, gaseous exchange takes place where CO2 diffuses out of the lungs and oxygen from the lungs will enter the blood.

This reoxygenated blood is taken through the pulmonary vein into the left side of the heart, which is thicker than the right as it has to be strong enough to pump the blood throughout the rest of the body (pulmonary circulation).

Each side of the heart has two connected chambers – an upper chamber or atrium and a lower chamber or ventricle. Each time blood is pumped from the veins into the heart, it enters the atria and is pumped down into the ventricles. From there, it leaves the heart via the arteries.

The valves of the heart

The role of the valves found in the heart is to prevent blood from flowing back to where it has been pumped from.

Atrioventricular valves

The heart has two atrioventricular (AV) valves: tricuspid and bicuspid.

The tricuspid valve acts as a conduit and barrier between the right atrium and ventricle. When the right ventricle contracts, this valve prevents blood returning to the right atrium.

The bicuspid (mitral) valve stops blood from flowing back from the left ventricle to the left atrium.

Semilunar valves

There are also two semilunar (SL) valves: the aortic valve and the pulmonary valve. 

Blood leaving the heart from the left ventricle enters the largest artery in the human body: the aorta. It is prevented from flowing back into the heart by the aortic valve.

When deoxygenated blood leaves the right ventricle and enters the pulmonary artery, which feeds into the lungs, the pulmonary valve prevents blood from flowing back into the right ventricle.

The Sino-atrial Node (SA Node)

This is located on the wall of the right atrium of the heart and its function is to regulate the heart, acting as a pace maker. It sends out an electrical pulse, which passes across the atria, causing them to contract and pump blood. 

The benefits of cardio workouts

The heart is the hardest working muscle in the body and for it to work efficiently, it needs to be healthy.

Regular cardiovascular exercise, whether working with a personal trainer, taking part in an aerobic class or joining a sports team, will strengthen the heart and improve blood flow (see our blog on Personal training: Cardio-vascular intensity). This will reduce the risk of cardiovascular disease and stroke, increase the removal of toxins from the body and allow more oxygen and nutrients to reach the cells.


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