Myocardial injury markers have not been routinely used to detect myocardial damage in children. Plasma cardiac troponin I (cTnI) is a sensitive & specific new marker of myocardial injury that is reportedly only found in patients with myocardial damage. cTnI was used to screen children without cardiac symptoms or clinically apparent cardiac disease who were examined in a pediatric outpatient clinic or emergency room. cTnI was measured by an FDA-approved immunoassay (Opus Troponin I, Behring Diagnostics), where levels≥0.5 ng/ml indicate myocyte injury, in 283 children (153 male/130 female, mean age 3.6 ± 4.2 yrs, range, 0.13-22.4 yrs). Plasma creatine kinase MB (CK-MB), total CK, & myoglobin were also measured. A retrospective chart review was performed. Plasma cTnI levels correlated with CK-MB (r = 0.22, p = 0.0008) but not with CK or myoglobin. 19/283 children (6.7%) had elevated cTnI. They were younger (mean age 1.88 vs. 3.6 years; p <0.0001) than the 264 children with undetectable cTnI. 15 of the 19 children (78.9%) with elevated cTnI had symptoms consistent with an acute viral infection. cTnI was elevated in 7.8% (95% CI: 4.4%, 12.5%) of 193 children with acute viral illnesses. Children with elevated cTnI were significantly younger, & had lower mean hemoglobin & hematocrit levels (p = 0.017 & 0.063, respectively) than children without cTnI elevations. The remaining 90 children were well, but 4.56% (95%CI: 1.2%, 11.1%) also had an elevated cTnI level. Although plasma was limited, all 4 children with cTnI >0.89 ng/ml who also had cTnT measured (Enzyamun assay, Boehringer Mannheim) for confirmation showed cTnT elevations. High-level cTnI elevations (>2 ng/ml), consistent with levels found in adults with acute myocardial infarction, were noted in 4 children. Of these, 3 had acute viral illnesses & were 2.3-3.1 yrs old, with cTnI levels of 2.61-2.86 ng/ml, & had diagnoses of upper respiratory infections, febrile seizure, or gastroenteritis. The fourth child was clinically well. None of these 4 children had congenital heart disease. One 7 month old child with a mild cTnI elevation had an ASD/VSD repair 6 mos earlier. In conclusion, cTnI elevations occur in children without cardiac symptoms or clinically apparent cardiac disease. For 6.7% of children presenting at outpatient hospital visits, these elevations were consistent with the myocardial injury seen in adults with unstable angina or acute myocardial infarction. Further prospective studies are warranted to determine the incidence, risk factors, & clinical significance of these findings,& whether they relate to the development of idiopathic cardiomyopathy in later life.