What occurs when the atria contracts?

When the atria contract, they push blood into the ventricles, which is why the ventricles fill with blood. This process is part of the cardiac cycle known as atrial systole, where the contraction of the atria helps ensure that the ventricles receive a sufficient volume of blood to pump out to the body and lungs during the subsequent ventricular contraction. This filling also helps maintain adequate preload, which is crucial for the ventricles to generate the appropriate stroke volume during their contraction.

Filling of the ventricles occurs before they contract, ensuring that the heart operates efficiently. The other options do not directly relate to the immediate action of atrial contraction. Blood being pumped to the lungs typically occurs during ventricular contraction, when the right ventricle pumps blood through the pulmonary artery. An increase in heart rate is a result of various factors such as exercise or conditions affecting the autonomic nervous system, rather than the simple action of atrial contraction. Lastly, while the opening and closing of heart valves are part of the overall function of the heart, atrial contraction does not directly cause valves to open; it depends on the pressure dynamics in the heart chambers and the timing of contractions.