What is the term for an early atrial or ventricular contraction?

The term for an early atrial or ventricular contraction is "Premature Contraction." This term specifically refers to instances where the heart experiences extra beats that occur earlier than the next expected heartbeat in a regular rhythm. These can manifest as either premature atrial contractions (PACs) or premature ventricular contractions (PVCs), depending on which part of the heart is involved.

Premature contractions are often a common occurrence and can be benign, especially in healthy individuals. They are distinct from other conditions, such as sinus bradycardia, which involves a slower than normal heart rate, or atrial flutter, which is characterized by a rapid heart rate due to abnormal electrical pathways in the heart's atria. Asystole refers to a state where there are no electrical impulses in the heart, leading to a total cessation of heart activity. Thus, the term "Premature Contraction" is the most appropriate to describe the early beats mentioned in the question.