The heart is crucial, irreplaceable for humans because it works tirelessly from birth to death. Its role is essential – heart ensures blood circulation in the bloodstream by contractions and the supply of oxygen to the cells, which is used for energy production and for life at all. The heart works like a regular pump never-ending, with which we can see some phases. These phases correspond to the gradual withdrawal of ventricular fibrillation. As for pumping water, also the heart is influenced by pulse - the rhythmical electrical discharges in the right atrium.