There are a number of types of PVC, which are classified according to different standards. For example, they may be classified according to how often the PVCs alternate with normal heartbeats:

Alternatively, more than one PVC may occur in a row and be classified as follows:

• Couplets: Two PVCs in a row.
  
  
• Runs of “nonsustained” V-tach (short for ventricular tachycardia): At least three PVCs in a row. In patients with weakened pumping function of the heart due to a prior heart attack, any runs of nonsustained V-tach indicate a high risk of potentially fatal arrhythmias (such as ventricular tachycardia or ventricular fibrillation). These cases usually require further evaluation by tests that might include cardiac catheterization and an electrophysiology study.

Furthermore, PVCs may be classified according to where they arise within the heart:

• Unifocal PVCs. The PVCs arise from the same source and appear similar on an electrocardiogram (EKG).
  
  
• Multifocal PVCs. The PVCs arise from different sources within the heart and look different from each other on the EKG.

The timing of the PVCs in relation to the normal beats is very important. Certain PVCs may occur in a pattern where they affect the ventricle just as it is recovering from the previous contraction. This is known as the vulnerable period of the ventricle. These PVCs are called R on T PVCs and may trigger lethal arrhythmias.

Other classifications also exist. Patients are encouraged to speak with their physician for more information about PVCs and their effect on the heart.