In an attempt to identify a group of blunt trauma victims with asymptomatic myocardial contusion (MC) who do not benefit from intensive cardiac monitoring, we prospectively divided 336 patients admitted to the SICU with possible MC following blunt trauma in the 6 years prior to January 1990 into three groups: Group 1 (n = 155, age 30.5 +/- 9 years) consisted of those patients admitted for mechanism of injury, J-point elevation, with or without minor chest injury. None developed arrhythmias. Their SICU length of stay (LOS) was 2.41 +/- 0.77 days. Group 2 (n = 43, age 31.5 +/- 10 years) patients had the same admission criteria as the patients in group 1 plus an abnormal emergency department ECG, i.e., arrhythmia, heart block, ischemia. None had cardiac complications. Their SICU LOS was 2.47 +/- 0.94 days. Group 3 (n = 138, age 40 +/- 20 years) patients had four or more rib fxs, a pulmonary contusion, a flail chest, or extra-thoracic injuries or were greater than 60 years of age. All required SICU admission for their non-cardiac injuries. Nineteen patients had cardiac complications requiring treatment. None had a cardiac death. Their SICU LOS was 10 +/- 22 days. We conclude that young patients with minor blunt thoracic trauma and a normal or minimally abnormal ECG do not benefit from cardiac monitoring.