One of the most common mechanism of tachyarrhythmias is re-entry. It is characterized by origin of an ectopic beat which then enters the circuit again and again causing tachyarrhythmia. The attached video exhibits the re-entry circuit. In addition, it also provides great description of the said mechanism. Reference: Davidson's Principles and Practice of Medicine Video Source: https://www.youtube.com/watch?v=FrdXIVwQx74