Myocardial damage in infancy is a risk factor for eventual cardiac disease. Given that myocardial stress is greatest during the perinatal period and that the neonatal period is when most pediatric heart failure occurs, the aim of this study was to determine whether even otherwise healthy neonates might have subclinical myocardial damage and, if so, what characteristics might identify them. Umbilical cord and neonatal serum samples from 32 normal neonates were assayed for biomarkers of myocardial injury. No neonate had clinical evidence of cardiac or other abnormalities. Serum cardiac troponin T was elevated in 19 of 25 cords (76%) and in 16 of 17 neonates (94%); levels indicating myocardial infarction (> or =0.2 ng/ml) were found in 2 patients (1 umbilical cord and 1 neonatal sample). Creatine kinase-MB was elevated in 6 of 16 cords (38%) and in 8 of 15 neonates (53%). Cardiac troponin I was elevated in 11% and 17% of samples, myoglobin in 4% and 17%, and high-sensitivity C-reactive protein in 9% and 40%. Measures of myocardial injury were associated with longer hospitalization (r = 0.50, p = 0.04), non-Caucasian race (p = 0.012), lower birth weights (p = 0.014), positive maternal cervical cultures (r = 0.41, p = 0.046), and elevated high-sensitivity C-reactive protein (r = 0.66, p = 0.005). In conclusion, clinically occult myocardial injury appears to occur in some healthy newborns, although whether it is pathologic or not remains to be determined.