In the past myocarditis has been suggested as a possible cause of repolarization abnormalities in sportsmen, but, to our knowledge, no direct in-vivo demonstration of this relationship has so far been found. We report the cases of three professional athletes with repolarization changes at rest and/or during exercise and mild segmental wall motion anomalies in the left ventricle on echocardiography, in whom myocarditis was diagnosed by non-invasive and invasive clinical investigations, including endomyocardial biopsy. We think that probably the frequency with which myocarditis is responsible for electrocardiographic and echocardiographic abnormalities in athletes has so far been underestimated, and that caution must be employed when interpreting minor segmental wall motion abnormalities on resting and exercise echocardiograms in trained subjects as being due to athlete's hart, especially when they present with repolarization changes.