One hundred twenty-five consecutive patients with a diagnosis of blunt chest trauma underwent T1-201 thallous chloride single photon-emission computed tomography (SPECT) scan, as well as physical examination, serial ECG and cardiac enzymes. A subset of patients had 24-h Holter monitoring. SPECT scan was performed within 24 h of injury. Seventy-five patients had positive scans and 48 had negative. Two studies could not be completed. Eleven patients with positive studies developed serious arrhythmias (multiple premature ventricular beats or atrial fibrillation). None of these patients had a prior history of cardiac disease. While three patients with negative SPECT scans had arrhythmias, each had a prior history of cardiac disease and two were on chronic antiarrhythmia therapy. Neither ECG findings, creatinine phosphokinase (CPK), nor CPK-isoenzymes distinguished between those patients who did and did not develop arrhythmias. We conclude that SPECT scan is useful in screening patients at risk of developing arrhythmias from cardiac contusion. Utilization of SPECT scan allows early discharge of a significant number of patients with blunt chest trauma who would otherwise require hospitalization for arrhythmia monitoring.