During c atrial diastole the ventricles contract forcing blood out of the heart. Lead I is calculated using data from the electrodes on both the right and left arm. The Cardiac Cycle And Ecg Segments Download Scientific Diagram Atrial and Ventricular diastole chambers are relaxed and filling with. . Systole is defined as the phase in which the heart especially the ventricles is contracting. The period of timethat begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle Figure 1931. It starts at the beginning of one heartbeat and ends at the beginning of another. The relaxed heart allows for blood to fill the cardiac chambers. The time interval from the beginning of one heartbeat to the beginning of the next heartbeat is called the cardiac cycle or T eg the time from one P wave to the next P wave. The period of relaxation that occurs as the chambers fill with blood is called di