The DDD pacemaker allows sensing and pacing in both chambers and can, therefore, maintain atrioventricular synchrony. However, this pacemaker creates an additional anterograde conduction system between the atrium and ventricle and, in the presence of ventriculoatrial (VA) conduction, the possibility of pacemaker-mediated tachycardia exists. A simple bedside technique that does not require catheterization or expensive equipment was used to detect VA conduction. Just after DDD pacer implantation, an attempt was made to detect VA conduction in 31 patients. Ambulatory monitoring (Holter) was done for 24 hours after implantation and at 2 to 4 and 6 to 8 weeks after implantation to detect pacemaker-mediated tachycardia. Attempts to induce pacemaker-mediated tachycardia were made using a special programmable external stimulator at follow-up after implantation. It was found that (1) all the 17 patients with detectable VA conduction had pacemaker-mediated tachycardia when the atrial refractory period was less than the VA conduction time, (2) pacemaker-mediated tachycardias were not inducible or detected spontaneously when atrial refractory period was equal to or greater than VA conduction time + 50 ms, (3) VA conduction was not detectable in 9 of the 17 patients at a later visit. Six of these 9 received antiarrhythmic therapy or had developed congestive heart failure. VA conduction has important implications in patients with DDD pacemakers and can be readily evaluated at the bedside.