Cardiac movements: systole and diastole

Ventricular contraction is known as systole and in it occurs the emptying of the ventricles. Ventricular relaxation is known as diastole and it is at this stage that the ventricles receive blood from the atria.

Ventricular contraction then forces blood to the pulmonary and aorta arteries, whose semilunar valves (three half-moon membranes) open to allow blood to pass through. Once inside these vessels, the return of blood (reflux) to the ventricles from the aorta and pulmonary arteries is prevented by the sudden closure of these same valves.