The center, located behind the left breast, is a muscle as big as a fist adult and weighs about 300 grams. It works like a pump that circulates 4 to 5 liters of blood throughout the body.  The cardiac contraction allows the injection of blood from the heart through the arteries to organs, and muscle relaxation allows the filling of the heart through veins. The pulse (on one wrist, neck…) gives an idea of heart function. The normal heart rate at rest is about 70 to 75 beats per minute. It is slower in men than in women, faster in children than in adults. There is talk of tachycardia when the pulse is fast and bradycardia when the pulse is slow. The atria, the ventricles and heart valves Within the heart, blood circulates through 4 cavities: 2 atria (right and left), 2 ventricles (right and left). The san from one headset to a ventricle through a hole whose opening is regulated by a system of valves called atrio-ventricular valves. When they are closed, they form a valve that prevents blood from flowing. It gets the blood from the atria and ventricles by the returns. There are also valves between the heart and arteries and veins. Thevalvular diseases are valves: openness can be narrowed and hinder the ejection of blood or closing incomplete and cause a leak.