During ventricular systole, oxygenated blood is pumped from the left ventricle into the aorta and deoxygenated blood is pumped from the right ventricle into the pulmonary trunk. The pulmonary trunk divides into two pulmonary arteries that supply deoxygenated blood to the lungs. Backflow of blood into the ventricles is prevented by the closure of atrioventricular valves.