Cardiac Cycle

 Cardiac Cycle

        The cardiac cycle consists of two interrelated phases: systole, the contraction phase, and diastole, the filling phase. During diastole, the ventricles fill with blood from the atria via open atrioventricular valves. he 526 SECTION II Intervention Strategies for Rehabilitation Coronary circulation. (A) left main (LM); (B) left anterior descending (LAD); (C) left circumlex (CX); (D) right coronary (RCA); (E) posterior descending (PDA). 

         The branches of the LAD are known as diagonals; the branches of the CX are known as marginals. atrioventricular valves lie between the atria and the ventricles and include the tricuspid valve on the right and mitral valve on the left. he first two-thirds of ventricular filling is passive; during the last one-third the atria contract and push the blood into the ventricles. his contraction is known as the atrial kick. After the atrial kick, diastole ends and the atrioventricular valves close. Systole begins with both the atrioventricular and semilunar valves closed. An initial isovolumetric contraction, similar to an isometric contraction of striated muscle, increases the pressure within the ventricles, and the semilunar valve opens. he LV then undergoes a concentric contraction, causing a volume to be ejected, termed the stroke volume (SV). After the SV is ejected, the aortic valve closes and systole is complete. he cardiac cycle is defined by the presence of normal heart sounds, S1 and S2. Heart sounds are associated with valvular closings; S1 is associated with atrioventricular valve closure, and S2 is associated with semilunar valve closure. Systole occurs between S1 and S2, and diastole occurs between S2 and S1