The heart is a unique muscular organ, consisting of two adjacent pumps, each divided into an upper atrium and a lower ventricle.

Contraction and relaxation of these chambers controls the volume and rate of blood circulating through the body.

The heart muscle (myocardium) is a power house.  It has to be strong enough to push the blood out to the extremities of the body, ensuring all tissues receive oxygen and nutrients.

Heart rate

We often become aware of our heart rate when it increases above the average of 60-90 beats per minute.

Our hearts have their own electrical system, the core of which is a small group of muscle cells known as the sino-atrial node (SAN) - the heart's natural pacemaker. 

Electrical activity in the SAN stimulates a wave of muscular contractions.  First the atria contract, then there is a short delay to allow the atria to complete their contraction before the ventricles contract. 

It is the contraction of the ventricles that is responsible for the main pumping action of the heart and the circulation of the blood.

Circulation system

From the heart, the blood travels through an extensive circulatory network of arteries, veins and capillaries. 

These vary from the aorta, the size of a garden hose, to the coronary arteries, the size of a ball point pen refill, down to the capillaries.  The force required to pump blood from the heart to minute capillaries in our feet is quite tremendous. 

Blood clots trying to pass through blood vessels can lead to a heart attack as they reduce or prevent the flow of blood to the myocardium, becoming lodged in the narrowing arteries.

20/05/2009