[[Image:parasystole_12lead.jpg|thumb|An example of parasystole on a 12 lead ECG]]
[[Image:Paraystole_rhythmstrip.jpg|thumb|This rhythm strip shows clear parasystole. Here the origin of the ectopic beats is somewhat distal to the HIS bundle.]]
Parasystole is the phenomenon that results from two competing pacemakers in the heart. Usually a supraventricular and nodal/ventricular pacemaker compete. For example, sinus rhythm might be interfered with by ventricular ectopic beats. The basic rhythm in this example would be sinus rhythm with a rate of 60/min. Ectopic ventricular complexes can be seen interfering with this rate and rhythm. Parasystole is diagnosed when the ectopic
beats have a constant RR interval, e.g. 1500ms, resulting in a rate of 20 ventricular ectopic complexes per minute. [[Fusion beats]] are often present as the two rhythms are dissociated.