Final answer:
The cardiac cycle is initiated by the sinoatrial node, which generates an electrical impulse leading to a pattern of contraction (systole) and relaxation (diastole) in the heart chambers. This cycle is regulated and carefully coordinated for efficient blood pump throughout the body.
Step-by-step explanation:
Initiation of the Cardiac Cycle
The cardiac cycle is initiated by the heart's natural pacemaker, the sinoatrial node (SA node). This cycle includes periods of contraction and relaxation known as systole and diastole, respectively. The SA node generates an electrical impulse that causes the atria to contract (atrial systole), pushing blood into the ventricles. This electrical signal is briefly delayed at the atrioventricular node (AV node), allowing the ventricles to fill before they contract (ventricular systole). The contraction of the ventricles pumps blood to the body and the lungs, and their subsequent relaxation (ventricular diastole) allows for the chambers to fill with blood again, hence preparing the heart for the next beat.
The rhythmic beats of the heart, known as sinus rhythm, are due to these regulated electrical signals. This ensures blood is pumped efficiently throughout the body. The lub and dub sounds are associated with the closing of heart valves during the cycles of systole and diastole.