What occurs during phase two of the cardiac cycle?

Phase two of the cardiac cycle refers to ventricular systole, which is the period during which the ventricles contract and pump blood out of the heart. During this phase, the electrical signal that originated from the Sinoatrial (SA) node progresses through the heart's conduction system, leading to the depolarization of the ventricular muscle. This contraction forces blood into the aorta from the left ventricle and into the pulmonary artery from the right ventricle.

The significance of this phase cannot be understated, as it is essential for maintaining effective circulation, delivering oxygen-rich blood to the body and deoxygenated blood to the lungs for oxygenation.

In contrast, atrial contraction occurs during phase one, which is when the atria contract to fill the ventricles with blood. Ventricular filling, on the other hand, occurs after ventricular systole when the ventricles relax and allow blood to flow in from the atria. The concept of resting potential is associated with the electrical state of cardiac cells during the diastolic phase, not a phase of the cardiac cycle itself. Therefore, ventricular systole accurately captures the main event of phase two, highlighting its critical role in the overall function of the heart.