ectopic heartbeat

Myocardial depolarization originating from myocardium distinct from the sinus node.

Specific

multifocal (chaotic) atrial tachycardia (MAT) premature ventricular complex (PVC) or depolarization (PVD), extrasystole wandering atrial pacemaker

References

Stedman's Medical Dictionary 27th ed, Williams & Wilkins, Baltimore, 1999