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The cardiac cycle is defined as a sequence of alternating contraction and relaxation of the atria and ventricles in order to pump blood throughout the body. It starts at the beginning of one heartbeat and ends at the beginning of another.
The cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0.8 seconds. Beginning with all chambers in diastole, blood flows passively from the veins into the atria and past the atrioventricular valves into the ventricles.
The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. [1] It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, called systole. [1]
The cardiac cycle is a series of pressure changes within the heart. These pressure changes result in blood movement through different chambers of the heart and the body as a whole. These pressure changes originate as conductive electrochemical changes within the myocardium that result in the concentric contraction of cardiac muscle.
The cardiac cycle can be divided into four stages: Filling phase – the ventricles fill during diastole and atrial systole. Isovolumetric contraction – the ventricles contract, but as the heart valves are shut, the volume remains constant.
The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle (Figure \(\PageIndex{1}\) ). The period of contraction that the heart undergoes while it pumps blood into circulation is called systole.
Define cardiac cycle, systole, and diastole. Describe the phases of the cardiac cycle including ventricular filling, isovolumic contraction, ventricular ejection, and isovolumic relaxation. Explain how atrial systole is related to ventricular filling.