A normal cardiac cycle begins with each heart beat, involves the flow of blood through the four chambers of the heart and has distinctive components or phases. The heart is a muscular organ that functions as the body's pumping station. Veins return blood from the body to the heart. During the cardiac cycle, the heart pumps blood to the lungs to receive oxygen. Oxygenated blood returns to the heart. The heart pumps blood out to the body through arteries.
Early Diastole
The heart is divided into four hollow chambers, the right atria, the right ventricle, the left atria and the left ventricle. The right chambers receive blood from the veins. The left chambers accept blood from the lungs. The left ventricle pumps blood into circulation. "The Encyclopedia for Nursing and Allied Health" classifies the first phase in the cardiac cycle as early diastole. During this phase, the ventricles are relaxed. The semilunar valves close and the atrioventricular valves open and the ventricles fill with blood.
Late Diastole
During this phase, the sinoatrial, or SA, node sends an electrical signal to the atria. The SA node is located in the right atrium and initiates the electrical impulse that triggers each heart beat. In late diastole, the atrium contracts and the ventricles fill with more blood. The electrical impulse is delayed at the atrioventricular, or AV, node to allow the ventricles to contract at one time. Passing through a network of specialized fibers called the AV bundle, the impulse triggers the ventricles to contract.
Systole
Systole occurs when the atrioventricular valves close. During this phase, the semilunar valves open allowing blood to be pumped out of the ventricles and into the aorta. Medicine Net says the aorta is the body's largest artery that carries blood from the left ventricle of the heart. The aorta is divided into branches that carry oxygenate blood to the head, neck, major organs of the body, arms, abdomen and legs.
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