What are the main stages of the cardiac cycle?

Blood enters the atria. It cannot pass into the ventricles because the atrioventricular valves are closed. The heart is in diastole.The atria contract. The pressure in the atria becomes greater than the pressure in the ventricles, and the atrioventricular valves open. Blood enters the ventricles. This is atrial systole.The ventricles contract. Pressure in the ventricles becomes greater than the pressure in the atria, and the atrioventricular valves close so that blood cannot return to the atria. Pressure in the ventricles becomes greater than the pressure in the aorta and pulmonary artery, so the semilunar valves open. Blood is ejected into the aorta and pulmonary artery. This is ventricular systole.