Final answer:
The cardiac cycle includes periods of diastole (relaxation) and systole (contraction), during which blood fills the chambers of the heart and is then pumped out during ventricle contraction. Most filling occurs during diastole, with atrial systole completing the process, before ventricular systole occurs as indicated by the QRS complex on an ECG.
Step-by-step explanation:
Understanding the Cardiac Cycle
The cardiac cycle is the sequence of events that occur in the heart from one heartbeat to the next. It includes periods of both contraction and relaxation, which are necessary for the efficient pumping of blood. During diastole, the heart muscle is relaxed and the chambers of the heart fill with blood. Next is atrial systole, where the atria contract to complete the filling of the ventricles. This is followed by ventricular systole, during which the ventricles contract, propelling blood out of the heart and into circulation.
It is essential for systole and diastole to be carefully regulated and coordinated. Most of the ventricular filling occurs passively during diastole, with the 'atrial kick' from atrial systole contributing to the final portion of ventricular filling. The volume of blood in the ventricles at the end of diastole, known as the end diastolic volume or preload, is crucial for determining the amount of blood that will be ejected from the heart during systole, known as the stroke volume.
The ECG (electrocardiogram) can provide a visual representation of the phases of the cardiac cycle, with the QRS complex signifying the onset of ventricular systole. Understanding the different phases and their duration helps in assessing heart function and diagnosing potential cardiac conditions.