==Compensatory or noncompensatory pause==
The duration of the interval following a premature
beat can help in the differentiation of a atrial or ventricular premature beat.
===Non-compensatory pause, following an atrial premature complex===
===Fully compensatory pause, following a ventricular premature complex===
The electrical activity of a ventricular premature complex is usually not conducted through the AV node towards the atria. The sinus node will not be reset. If the next sinus complex finds the AV nodal tissue still refractory (and thus not conducting) there will be a pause until the next sinus complex follows. The interval between the premature ventricular complex and the next sinus complex will be longer (longer than 1 second in the above sample of a heart rate of 60/min). This is called a fully compensatory pause. With the use of a caliper, the preceding sinus rate can be tracked beyond the ventricular premature complex. This is a telltale sign of a ventricular premature complex without retrograde conduction.
[[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
beats per minute. [[Fusion beats]] are often present as the two rhythms are dissociated.