Which part of the EKG shows the contraction of the ventricles?

The QRS complex represents the electrical activity associated with the contraction of the ventricles in the heart. This part of the EKG waveform indicates depolarization of the ventricles, which leads to their contraction and the pumping of blood out of the heart. The QRS complex is typically characterized by its steep upward and downward deflections, reflecting the rapid electrical conduction that occurs as the ventricles contract.

The other components of the EKG, such as the T wave and P wave, represent different aspects of the cardiac cycle. The T wave indicates ventricular repolarization, the recovery phase following contraction, while the P wave shows atrial depolarization, which occurs before ventricular contraction. The U wave, though less commonly observed, may represent further repolarization of the ventricles or possibly other myocardial electrical activity. Therefore, the QRS complex is specifically associated with ventricular contraction, making it the correct answer in this context.