What occurs in the heart when the atria contract?

When the atria contract, their muscular walls contract and this action helps to push blood into the ventricles. This phase of the cardiac cycle is known as atrial systole. During this contraction, the pressure in the atria increases, forcing blood through the open atrioventricular valves (the mitral and tricuspid valves) and into the relaxed ventricles below. This process fills the ventricles with blood in preparation for the next phase of the heartbeat, which is ventricular contraction.

The other options do not accurately depict what occurs during atrial contraction. The pumping of blood into the lungs or the body occurs during ventricular contraction, not during atrial contraction. Additionally, blood being drawn into the atria happens during ventricular diastole when the ventricles are filling with blood, not during the atrial systole phase. Thus, the correct understanding of atrial contraction is crucial for comprehending the overall mechanics of the heart's function.