Standardized telemetry during swimming and blood pressure monitoring were performed on 25 consecutive patients (22 men and 3 women: mean age 59 +/- 7 years) after myocardial infarction, sustained on average 28 +/- 26 months ago. Mean exercise tolerance, as judged by symptoms during bicycle ergometry, was 1.31 +/- 0.5 W/kg (pulse limit 117 +/- 21 beats/min). The swimming test had to be discontinued in six patients because of severe arrhythmias, in two because of severe angina. Seven patients completed the full swimming distance, but were also considered unsuitable for swimming because of moderate angina and dyspnoea. Ten patients proved to be fit for swimming. Their average ergometrically determined exercise tolerance (1.27 +/- 0.51 W/kg, pulse limit 114 +/- 16 beats/min) was not different from that of unfit patients (1.34 +/- 0.50 W/kg; 119 +/- 24 beats/min). During swimming the unfit patients had a significantly higher heart rate and blood pressure rise than the fit ones. Only in the unfit patients the exercise tolerance limit determined by bicycle ergometry was exceeded during swimming. This indicates that postinfarction patients should undergo swimming telemetry before declared fit for swimming.