Ventricular systole describes the action in which the left lower chamber or ventricle of the heart contracts and pushes blood through the body during the cardiac cycle, according to WebMD. The systolic phase is countered by the diastolic phase, which occurs when the ventricle relaxes and fills with blood.
The heart consists of two upper chambers, or atria, and two lower chambers called ventricles, explains Johns Hopkins Medicine Health Library. Blood flowing in and out of the chambers is regulated by four cardiac valves. The right ventricle is responsible for pumping deoxygenated blood from the right atrium to the lungs where the blood is oxygenated. From the lungs, the blood flows into the left atrium, and then to the left ventricle, which sends oxygenated blood through the arteries to nourish the body.
The word systole, which has been used since the 1500s to describe the mechanics of the heart, is derived from a Greek word meaning "contraction," according to MedicineNet. Blood pressure readings indicate systolic pressure as the top number and diastolic pressure as the bottom number. Normal systolic pressure is below 120, according to WebMD; a reading higher than 140 is considered hypertension. Normal diastolic pressure is between 80 and 90.