During the systole phase of the cardiac cycle, the left ventricle contracts and blood is pumped into the aorta. Which of these valves prevents a backflow of blood into the left atrium?
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.
