The Cardiac Cycle is the Sequential Contraction and Relaxation of atria and ventricles Ventricular systole is initiated by 13 Ventricular excitation ontic valve closes Aortic (1)Isovolumic contraction pressure The interval between the start of Mitral ventricular systole and the opening of the semilunar valves is called isovolumic eft atrial pressu contraction because ventricular volume isi,A constant during this brief period. Ventricular pressure rises abruptly 220The Cardiac Cycle is the Sequential Contraction and Relaxation of Atria and Ventricles (1) lsovolumic contraction Ventricular systole is initiated by Ventricular excitation • The interval between the start of ventricular systole and the opening of the semilunar valves is called isovolumic contraction because ventricular volume is constant during this brief period. • Ventricular pressure rises abruptly