Final answer:
The rapid depolarization phase in the ventricular action potential is represented by the QRS complex on an ECG, indicating the start of ventricular systole as the ventricles contract.
Step-by-step explanation:
The rapid depolarization phase in the ventricular action potential appears in the electrocardiogram (ECG) as the QRS complex. This large complex represents the depolarization of the ventricles, which requires a strong electrical signal due to the larger size of the ventricular cardiac muscle. The ventricles begin to contract as the QRS reaches the peak of the R wave, signaling the start of ventricular systole. It is important to note that the repolarization of the atria occurs during the QRS complex, but this process is masked on an ECG by the QRS signal. Following the QRS complex, the T wave represents the repolarization of the ventricles, marking the beginning of ventricular diastole.