In order to evaluate the incidence and significance of inducible supra-ventricular (SVTA) in patients with chronic myocardial infarction (MI), the results of systematic programmed atrial stimulation were compared in two groups of patients: 150 patients (group I) without MI or underlying heart disease, studied for syncope or conduction disturbances, 296 patients (group II) studied after an acute Mi (greater than 1 month). None of them had spontaneous SVTA, and 24-h Holter monitoring showed no SVTA. The atrial stimulation programme used one and two extra stimuli delivered during sinus rhythm and atrial pacing (600 ms and 10% less than the sinus cycle length). A sustained (S) (greater than 30 s) supraventricular tachycardia (SVT) (atrial flutter, fibrillation, tachycardia) was induced in 17 patients in group I (11%) and in 120 patients in group II (40.5%). In group II inducible SVTA could not be correlated with the occurrence of a SVT during acute MI, the location of MI, the value of LV ejection fraction (EF), the incidence of inducible sustained ventricular tachycardia (VT), or fibrillation (VF). However, inducible SVTA could be correlated with a significantly shorter effective atrial refractory period (197 +/- 23 ms vs 220 +/- 35 ms, P less than 0.001) and a shorter retrograde block cycle length (518 +/- 215 vs 585 +/- 215 ms, P less than 0.03). The patients in group II were followed-up for at least 6 months; 12 of them developed sustained episodes of supraventricular tachycardia; 11 of them had inducible SVTA (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)