The heart pumps: ventricular ejection. As the ventricles contract, they generate enough pressure to open the semi- lunar valves and push blood into the arteries. The pressure created by ventricular contraction becomes the driving force for blood flow. High-pressure blood is forced into the arteries, displacing the low-pressure blood that fills them and pushing it farther into the vasculature. During this phase, the AV valves remain closed and the atria continue to fill.