Premature beats, also known as premature contractions, abbreviated as premature beats, are a type of early ectopic heartbeats. They can be classified according to their origin into sinus, atrial, junctional, and ventricular, with ventricular being the most common. Premature beats are a common type of ectopic rhythm that can occur on the basis of sinus or ectopic rhythms, such as atrial fibrillation. They can occur occasionally or frequently and may irregularly or regularly follow each or several normal beats, forming a bigeminy or trigeminy pattern of premature beats. Generally, sinus, atrial, and junctional premature beats do not involve rapid ventricular rates and are usually not life-threatening. Although most premature beats are functional and do not cause damage to the heart, some pathological premature beats occurring on the basis of structural heart disease may further induce arrhythmias. In particular, ventricular premature beats may provoke ventricular tachycardia or ventricular fibrillation and in severe cases, may lead to sudden cardiac death. Additionally, multifocal atrioventricular premature beats are often a precursor to atrial fibrillation.