How the Heart Works: How the Heart Pumps

Imagine the heart to be like a hose with a one-way valve in it.

If you squeeze your hand around the hose it will push the blood out forcing the valve to open.

When you relax your hand, the valve will close. Although the valve is closed the blood still flows forward, but not as much as the flow which came out of the hose when the valve was open. The flow is still enough to keep the blood circulating throughout the cardiac cycle.

The act of squeezing the hand is similar to a heart contraction, or what we refer to as systole (systolic). The act of relaxing the hand is similar to heart relaxation, or diastole (diastolic).