Final answer:
A premature ventricular contraction (PVC) is an ectopic impulse that occurs early in the cycle and originates from the ventricle. It disrupts the normal rhythm of the heart.
Step-by-step explanation:
An ectopic impulse that occurs early in the cycle and originates from the ventricle is called a premature ventricular contraction (PVC). PVCs are abnormal electrical signals that cause the ventricles to contract earlier than expected, disrupting the normal rhythm of the heart. PVCs can be caused by various factors such as localized ischemia, certain drugs, or pathological conditions.