After successful resuscitation from cardiac arrest, it is important to identify whether the event has been triggered by a myocardial infarction, since this determines subsequent investigations and management. Previous studies have shown that biochemical indices of infarction become elevated after resuscitation in patients without myocardial infarction. This can lead to overdiagnosis of myocardial infarction in the post-arrest setting. The cause of the elevated enzyme levels is not known, but may involve electrical or mechanical injury to the heart during resuscitation. In this study we aimed to identify the effects of isolated direct current shock on serum levels of creatine kinase (CK), MB creatine kinase mass (MB-CK), and troponin T, and examined the relationships between enzyme levels and the dose of electrical energy used. Thirteen patients were studied who underwent DC cardioversion for atrial fibrillation. Serum was obtained for CK, MB-CK and troponin T estimation before and 10 min after cardioversion, at hourly intervals for 8 h, and 18 h after cardioversion. Total serum CK became significantly elevated after only 3 h and rose to a peak of 1294.4 IU l(-1) (P < 0.02) at 18 h. Post-shock CK levels were strongly correlated with total shock energy (r = 0.8, P < 0.01). Serum MB-CK was significantly elevated at 18 h among patients receiving total shock energies greater than 1000 J than in those receiving lower doses, reflecting a positive correlation (r = 0.64, P < 0.05) between shock energy and peak MB-CK level. Troponin T levels were not significantly elevated after cardioversion. In conclusion, total serum CK levels become significantly elevated early after cardioversion, suggesting rapid wash-out from injured skeletal muscle. MB-CK levels become significantly elevated in individuals receiving high energy shocks, probably due to release of small quantities of the CK-MB isoform from skeletal muscle. The negligible troponin T levels seen after high energy cardioversion indicate that significant myocardial injury does not occur. Electrical injury is not likely to account for the elevated troponin T levels seen after out-of-hospital resuscitation in patients without myocardial infarction.