Thirty-five patients with previous myocardial infarction underwent a programme of supervised physical rehabilitation. Twenty-two patients achieved a training effect (TE), after rehabilitation, i.e. a decrease of the double product (DP) for corresponding work loads and an increase of their physical work capacity (PWC). Thirteen patients, despite the absence of any clinical signs of decreased performance, did not obtain the above mentioned haemodynamic effects. In all of the patients the ejection fraction (EF) both at rest and during exercise was measured using a nuclear stethoscope. In patients with TE, the EF was 57 +/- 5% at rest, and 64 +/- 9% during exercise; in patients without TE the EF was 52 +/- 8% at rest and 46 +/- 10% during exercise. The correlation between TE (delta% PWC) and EF at rest and during exercise respectively, is positive and statistically significant, but there is a higher (r = 0,73) and more significant (p less than 001) correlation between delta% PWC and EF during exercise.