We studied one hundred consecutive patients, under the age of 55 years (mean age: 45.6 years), with myocardial infarction and a Q wave, in order to assess the prognostic value of an early stress test. Thirty five patients were excluded: 2 deaths, 21 revascularizations during the acute phase, 4 tests were performed without treatment, 6 tests were unable to be performed and 2 patients left hospital against medical advice. Sixty five patients [males, n = 60 (92.2%), anterior infarction, n = 25 (38.5%), thrombolysed n = 35 (53.8%), intact left ventricular ejection fraction (mean: 54.7%)] systematically underwent a stress test limited by symptoms, in hospital, on the tenth day of infarction, using an ergometric bicycle and under medical treatment (including beta blockers n = 47 (72.2%)] and cardiac catheterization. The test was considered positive when it was accompanied by angina and/or ST depression (n = 19), negative in the absence of these criteria for a level of 120 watts (n = 23), inadequate when the duration was less than 9 minutes and when the heart rate was less than or equal to 70% of the theoretical maximal heart rate (n = 11), doubtful when there was accentuation of ST elevation in the infarcted territory with mirror ST depression (n = 12). Only 30.7% of patients had multi-vessel coronary lesions (two- and three-vessel disease). The mortality was 4.6% with a mean follow-up of 27.4 months (range: 3-38). The sensitivity of the test for detection of multi-vessel disease was 62.5%, the specificity was 65.3%, the positive predictive value was 52.6%, and the negative predictive value was 73.9%. The sensitivity of this test, with beta-blocker treatment, to predict coronary lesions or cardiac events, fell to 33.3% and 37.5%, respectively. The stress test during the post-infarction period, with beta-blocker treatment, appears to be less sensitive for the identification of multivessel disease and cardiac events: this treatment should therefore be suspended before performing this test when allowed by the patient's clinical state.