Over a nine-month period, patients with chest trauma were prospectively evaluated for myocardial contusion. Ninety-two patients with evidence of anterior chest trauma were entered into the study and had 1) an ECG on admission and daily for three days; 2) monitoring of the myocardial band fraction of creatine phosphokinase (CPK-MB) on admission and every eight hours for 24 hours; 3) continuous electrocardiographic Holter monitoring for three to five days; and 4) noninvasive pulsed-Doppler cardiac output measurements daily for three days. Twenty-three patients developed 25 significant arrhythmias (SARRs): 1 atrial fibrillation, 1 AV dissociation, 5 supraventricular tachycardias, and 18 paroxysmal ventricular tachycardias. Cardiac outputs were significantly higher in those patients without SARRs. The CPK-MB levels correlated with the SARRs but were neither sensitive nor specific. No patients required specific therapy and none developed adverse sequelae of the SARRs. We conclude that 1) CPK-MB monitoring should not be routinely used for screening and diagnosis; 2) continuous arrhythmia monitoring deserves further clinical investigation but not routine application; 3) stable patients at risk for myocardial contusion should be monitored for 24 hours; and 4) the Abbreviated Injury Score for "minor" myocardial contusion should be deleted for purposes of ISS tabulation.