Objective: To establish normal values and determine the impact of congenital or acquired heart disease on serum cardiac troponin I (cTnl). Methods: Concentrations of cTnl were measured in two groups of children. Group A represented ambulatory pediatric patients with no apparent cardiac disease (n = 120) and patients in stable condition with known congenital or acquired cardiac abnormalities (n = 96); group B was composed of patients admitted to intensive care units with normal echocardiograms (n = 16), with abnormal echocardiograms (n = 36), and those with blunt chest trauma who were thought to have cardiac contusions (n = 7). Results: The cTnl concentrations were generally less than 2.0 ng/ml in group A and frequently below the level of detection for the assay (1.5 ng/ml). There was no statistical difference between the two outpatient subgroups (p = 0.66). Nine intensive care patients had cTnl values greater than 2.0 ng/ml. Six of these patients, all with abnormal echocardiograms, had values less than 7.7 ng/ml. All improved and had subsequent normal cTnl concentrations. None of the three remaining patients (two with systemic illness (trauma and Sepsis) and one with severe pulmonary hypertension), all with values greater than 8.0 ng/ml, survived. Three of the four patients with high likelihood of cardiac contusion had cTnl concentrations greater than 2.0 ng/ml (including one patient who died). Conclusions: Cardiac troponin-I values are generally not elevated in children with stable cardiac disease or general pediatric conditions. In the context of severe acute illness, significant elevation of cTnl may be an indicator of poor outcome. Elevation of cTnl may also have diagnostic value in cases when cardiac contusion is suspected.