To determine the rate of induction, specificity and evolution of electrically induced postmyocardial infarction ventricular arrhythmias, 10 dogs that underwent a sham operation and 20 dogs with experimental transmural apical myocardial infarction underwent serial closed chest electrophysiologic studies with programmed ventricular stimulation under light anesthesia 1, 2, 4 and 6 weeks after the operation. The reproducibility of the electrically induced ventricular arrhythmias was at a maximum when three extrastimuli were used during ventricular pacing for induction. The reproducibility of the arrhythmias was also a function of the age of the infarct. Electrically induced sustained monomorphic ventricular tachycardia, observed in 45 to 50% of the animals, was a highly specific postinfarction finding (0% specificity in control animals, regardless of the mode or timing of programmed cardiac stimulation), whereas nonsustained polymorphic ventricular tachycardia was not. The specificity of induced ventricular fibrillation was a function of the mode and timing of programmed stimulation. The rate of induction of the electrically induced ventricular arrhythmias did not change significantly during the 6 week period after myocardial infarction. A large infarct size (determined by postmortem examination) and a low left ventricular ejection fraction (determined during premortem cardiac catheterization) were the only variables identified that predisposed the animals to electrically induced sustained monomorphic ventricular tachycardia. These factors, however, did not correlate with the presence of electrically induced ventricular fibrillation or nonsustained ventricular tachycardia.