Our advanced cardiology series of courses have covered two mechanisms for the onset of supraventricular tachycardia and ventricular tachycardia. In this course, we examine a third mechanism: abnormal automaticity. This course will focus on focal atrial tachycardia, inappropriate sinus tachycardia, ventricular tachycardia, and patients who experience a high burden of premature ventricular complexes (PVCs). We review the underlying mechanisms, examine the epidemiology of these arrhythmias, and apply our understanding of the pathophysiology of abnormal automaticity-driven arrhythmias to identify appropriate treatment options for patients experiencing these conditions.