Systole is the phase of the cardiac cycle when the heart muscles contract, pumping blood out of the heart. This process occurs in both the atria and ventricles, with the ventricles contracting to send oxygen-rich blood to the body and deoxygenated blood to the lungs. During systole, the heart valves close to prevent backflow, ensuring that blood flows in the correct direction. The duration and strength of systole are crucial for maintaining adequate blood pressure and circulation throughout the circulatory system. Proper systolic function is essential for overall heart health.