Figure 3. The nonconducted premature atrial contraction triggered another transient episode of third-degree atrioventricular block, and ventricular asystole was terminated by pacing. The long P-P pause and the block of the second atrial impulse (marked as *) created a linking phenomenon that persisted for 5 cycles. The His potential was recorded, indicating that the block site was distal, at the infra-His-Purkinje system (paper speed 100 mm/s). HIS – His bundle; CS – coronary sinus; RVa – right ventricle