Question

repeated contraction and relaxation of both atria and ventricles​

Answer 1

Explanation:

Cardiac Cycle.

During the cycle, each of the four chambers goes through a contraction, called the systole, and a relaxation, called the diastole. In the first phase of the cycle both atria contract, the right first, followed almost instantly by the left. This contraction fills the relaxed ventricles with blood.

Answer 2

Answer:

Cardiac Cycle.

During the cycle, each of the four chambers goes through a contraction, called the systole, and a relaxation, called the diastole. In the first phase of the cycle both atria contract, the right first, followed almost instantly by the left. This contraction fills the relaxed ventricles with blood.