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Implantation of a VDD pacemaker (ventricular pacing; dual sensing [atrial and ventricular]; dual response [triggered + inhibited]) together with a single VDD electrode catheter restores synchronous AV ventricular stimulation in patients with higher-grade AV block and intact sinus function. If higher-frequency stimulation occurs it may be a sign of pacemaker malfunction or of inadequate pacemaker programming. This study was undertaken to determine, at first follow-up examination, in how many patients with a VDD pacemaker VVI stimulation occurred more than 5% of the time; how such patients differed from those with 5% or fewer VVI stimulations; and whether a changed program reduced the proportion of VVI stimulations.67 consecutive patients were tested 1 to 3 months after implantation of the Unity VDD pacemaker (Sulzer Intermedics). The frequency of VVI stimulations was determined via a diagnostic pacemaker memory store. After intermediate analysis, programming was optimized and the patients then re-tested 12 months after the initial implantation.At the first follow-up examination 54 patients had VVI stimulations ofor = 5% (0.5 +/- 0.9%) and 13 had5% of the time (19.8 +/- 10.7%). The two groups differed significantly from one another in their lower intervention frequency (or = 5% VVI stimulations: 47 +/- 6/min;5% VVI stimulations: 58 +/- 5/min). In particular, the pacemakers in patients with5% VVI stimulations had been significantly more often programmed to values of50/min. As a result, the pacemakers of these patients were reprogrammed to a lower frequency. A year after implantation there was no longer any difference in the lower intervention frequency, 44 +/- 4/min, between patients with initially5% VVI stimulations and those with initiallyor = 5% stimulations. At the same time, the proportion of VVI stimulations fell to 4 +/- 6%, with 67% of patients having AV synchronicity of95%.At first follow-up, patients with5% VVI stimulations differed from those withor = 5% stimulations with regard to an increased lower intervention frequency. In most of these patients the proportion of AV stimulations was increased to95% by reducing the lower intervention frequency toor = 50/min.