To determine the prevalence of myocardial ischemia before out-of-hospital cardiac arrest (OOHCA), we determined the prevalence of elevated cardiac troponin-T levels in subjects at the time of OOHCA. Plasma was collected from 63 subjects during resuscitation. Troponin levels were elevated (> or =0.03 ng/ml) in 25 subjects (39.7%; 95% confidence intervals [CI] 29% to 52%). Increasing age was associated with elevated troponin (OR 1.10; 95% CI 1.04 to 1.17). Elevated troponin levels did not reliably predict short-term outcome. Because troponin increases hours after the onset of ischemia, these data reveal that about 40% of OOHCA cases can undergo intervention before collapse.