What looks like simple bigeminy is actually a slightly more interesting diagnosis. Again, calipers are very helpful!

Notice that the ventricular complexes occur at a regular interval, and that the coupling interval (the space between the preceding QRS and the PVC) is not constant, as would happen with bigeminy. This rhythm is an independent ectopic ventricular rhythm, parasystole. Notice that the 6^th complex is a fusion beat (a combination of the sinus beat and the ventricular beat) – a sure indicator of an independent ventricular rhythm.

Traditionally parasystole is felt to represent a “protected” focus that is isolated from, and thus independent of, the electrical activity of the surrounding myocardium.   Parasystole is of no greater clinical import than PVCs of similar frequency or even bigeminy.