Second degree entrance block in intermittent ventricular parasystole

In a 21-year-old healthy man, there may be a second degree entrance block occasionally of 2:1 nature resulting in intermittent ventricular parasystole. The refractory period of the ventricular-ectopic (V-E) junction in this case was markedly longer than the ventricular muscle except the V-E junction, but much shorter than the whole length of the parasystolic cycle.