A. Atrial contraction occurs during atrial systole and is represented by the P wave, not the T wave, so it is unrelated to the danger of PVCs at this point. B. Maximum ventricular emptying happens during ventricular systole, particularly in early repolarization, but it is not the high-risk phase associated with the T wave. C. Depolarization refers to the QRS complex for ventricles, not the T wave, so PVCs during this phase do not carry the same risk as during repolarization. D. Repolarization of the ventricles occurs during the T wave. PVCs that fall on the T wave (known as the “R-on-T phenomenon”) can disrupt repolarization and trigger life-threatening arrhythmias such as ventricular tachycardia or ventricular fibrillation.