Question

multiple choice question
when the ____ contract, blood is forced into the ____ through the open av valves.
atria; ventricles
atria; pulmonary trunk
ventricles; aorta
ventricles; atria

Explanation:

The atria contract first in the cardiac cycle. When they contract, the atrioventricular (AV) valves are open, and blood is forced from the atria into the ventricles.

Answer:

A. atria; ventricles