Exercise testing is generally accepted for prognostic assessment of patients after infarction, but the prognostic value of transient myocardial ischemia during ambulatory electrocardiographic monitoring remains controversial. Of 281 consecutive postinfarction patients, 173 patients (132 men, 41 women) were prospectively studied with 24-hour Holter monitoring 14 +/- 5 days after acute myocardial infarction, and with submaximal exercise testing after 15 +/- 7 days. Patients with either conduction disturbances or pacemaker rhythm and 71 patients with digitalis medication were excluded. Myocardial ischemia was defined as horizontal or descending ST depressions or transient ST elevations > or = 0.1 mV with or without angina pectoris. The follow-up period was 1 year. Myocardial ischemia was observed in 40 patients (23%) during Holter monitoring, and 96% of the episodes were asymptomatic. Ischemia occurred during exercise testing in 46 patients (27%), two thirds of whom had no symptoms. Ischemia was detected by both methods (group A) in 19 patients (11%), with exercise testing only (group B) in 27 patients (16%), and with Holter monitoring only (group C) in 21 patients (12%). In 106 patients (61%), ischemia could not be ascertained at all. The 4 groups were comparable with regard to sex and age distribution, coronary risk factors, and medication. During follow-up, 50 patients (29%) experienced clinical cardiac events: 6 patients died, 7 had recurrent myocardial infarction, 14 developed unstable angina pectoris and required immediate revascularization, and 23 patients had recurrent but stable angina.(ABSTRACT TRUNCATED AT 250 WORDS)