It consists of two fundamental moments:
- diastole → filling
- systole → emptying
The blood flows to the atria through the pulmonary veins and the superior vena cava; the atrioventricular valves are initially open and the semilunars closed (the semilunar ones enter the large efferent vessels, pulmonary trunk and aorta). The blood then flows into the ventricles simply by gravity; when the ventricle is filled for 2/3 part the impulse (from the sinoatrial node to the internodal pathways) to the contraction of the atria which thus push the residual blood into the ventricles completing their filling. The atrioventricular valves passively close thanks to the pressure generated by the blood itself in the ventricle (to better understand the configuration of the atrioventricular valves).
The electric impulse reaches the atrioventricular node (where it undergoes a slowing down) and then the beam of His; the electrical impulse is distributed faster to the papillary muscles and then to the rest of the ventricle wall. We have ventricular systole. The semilunar valves open as a result of the increase in pressure exerted by the blood while the atrioventricular valves are tightly closed for the papillary muscles, which, as we have said, occur first in terms of time with respect to the rest of the contraction of the ventricular myocardial tissue.