The diagnosis and clinical significance of blunt cardiac injury remains controversial. Cardiac troponin I is not found in skeletal muscle and has a high sensitivity for myocardial ischemia or injury. We hypothesized that normal troponin levels 4 to 6 hours postinjury would effectively exclude the diagnosis of cardiac contusion. A prospective evaluation of all blunt trauma patients older than 16 and admitted with the possible diagnosis of blunt cardiac injury was undertaken. Patients in whom this diagnosis was considered had an electrocardiogram (EKG) on admission, serum troponin, CPK and isoenzymes 4 to 6 hours postinjury, and admission with overnight telemetry. Other laboratory data and radiographic imaging was obtained as indicated. Seventy-two patients met criteria for entry into the study. Data was incomplete or inaccurately obtained on six patients, and they were excluded. Forty patients had normal troponins and normal EKG's on admission and were discharged the following day without any untoward effect. Sixteen patients were admitted with abnormal EKGs. All of these 16 patients had normal troponins 4 to 6 hours after their injury. They all did well and were discharged the following day. Ten patients had elevated troponins 4 to 6 hours after injury. One died two days later from refractory cardiogenic shock. Another was noted to have severely depressed left ventricular function by echocardiography. The other eight patients sustained no cardiac sequelae and were discharged once recovered from injuries. In the hemodynamically stable patient a normal troponin 4 to 6 hours after injury excludes clinically significant blunt cardiac injury. This holds true whether the admission EKG is normal or not. An elevated troponin does not definitively diagnose a clinically significant contusion. However, these patients should be monitored at least for 24 hours. Patients suspicious for cardiac contusions who have normal troponins and no other serious injuries may be safely discharged to go home from the emergency department.