The heart contracts in two stages. In the first stage the Right and Left Atria contract at the same time, pumping blood to the Right and Left Ventricles. Then the Ventricles contract together (called systole) to propel blood out of the heart.

How do both atria contract simultaneously?

The pacemaker sets the normal rhythmic beat of the heart by coordinating the contractions of the heart chambers. The pacemaker first sends a signal along specialized cardiac muscle fibers in the walls of both atria to make them contract simultaneously.

Does the heart contract all at one?

The heart muscle contracts in two stages to squeeze blood out of the heart. This is known as systole. In the first stage, the upper chambers (atria) contract at the same time, pushing blood down into the lower chambers (ventricles). ... The heart muscle contracts in two stages to squeeze blood out of the heart.