Passive refilling of the heart occurs during which phase of the cardiac cycle?

At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). blood is flowing into the right atrium from the superior and inferior venae cavae and the coronary sinus. blood flows into the left atrium from the four pulmonary veins. the two atrioventricular valves, the tricuspid and mitral valves, are both open, so blood flows unimpeded from the atria and into the ventricles. approximately 70–80 percent of ventricular filling occurs by this method. the two semilunar valves, the pulmonary and aortic valves, are closed, preventing backflow of blood into the right and left ventricles from the pulmonary trunk on the right and the aorta on the left.