What happens during ventricular depolarization?

During ventricular depolarization, the cardiac muscle cells of the ventricles undergo a significant electrical event. This process initiates when an electrical impulse from the atrioventricular node spreads through the ventricles, leading to their contraction. This contraction is crucial as it forces blood out of the ventricles: the right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery, while the left ventricle sends oxygenated blood to the rest of the body through the aorta.

Understanding ventricular depolarization is critical because it marks the completion of the electrical cycle that initiates heart muscle contraction, driving blood circulation throughout the body. The other choices relate to different phases of the cardiac cycle, not specifically highlighting the event of ventricular depolarization. For instance, atrial contraction occurs prior to ventricular depolarization, making it an unrelated phase, while the filling of the ventricles occurs in a separate phase known as diastole. The heart rate can vary due to numerous factors but is also not directly tied to the mechanical actions associated with ventricular depolarization itself.