Duplex and triplet rhythms refer to a pattern of premature ventricular beats, such as a normal rhythm followed by a sinus rhythm followed by a premature ventricular beat, followed by a sinus rhythm, followed by a premature beat, and so on. A triplet rhythm is when two sinus rhythms are followed by a premature ventricular beat, followed by two normal sinus rhythms, followed by a premature beat, and so on. The main difference is in the electrocardiogram, but it is more difficult to distinguish the symptoms and clinical manifestations, and the treatment principles are generally the same.