Recent legislation has led to increasing numbers of car occupants wearing seat belts and presumably the number of injuries attributable to seat belts will also increase. The commonest such injury is a fracture of the sternum, and blunt myocardial damage is a logical sequel although often unsuspected and therefore unsought. Confirmation is difficult and ECG changes are usually absent or not specific. In three consecutive patients admitted with a fractured sternum we found raised blood levels of CK-MB (creatine kinase-myocardial band) and believe these indicate myocardial contusion. We therefore feel that an isolated fracture of the sternum should be considered a more serious injury than is initially apparent, as these patients are at risk of developing cardiac complications.