Background: Elevation of cardiac troponin I in the serum is a specific marker for myocardial injury. We measured levels of troponin I in the serum in children before and after cardiac catheterization to determine if this procedure was associated with an increase in levels of troponin. Methods: We enrolled patients under 21 years of age undergoing cardiac catheterization at our institution. A baseline sample of serum was drawn at the start of the procedure. Repeat samples were obtained immediately after, and six hours subsequent to the procedure. All samples were analyzed for cardiac troponin I using the Abbott AxSYM microparticle immunoassay system. Levels were considered normal (0–0.4 ng/ml) or elevated (>0.4ng/ml). Patients were excluded if the baseline level was elevated. Results: Levels of cardiac troponin I were elevated in the serum from 11 of 14 (79%) cases immediately after the procedure (p < 0.0001), and in 12 of 14 (86%) six hours later (p < 0.0001). Only 2 patients had recognized complications potentially causing myocardial injury. Conclusion: Levels of cardiac troponin I increase in the serum in a high proportion of children after cardiac catheterization. These elevations can be observed immediately, and are maintained for at least six hours. Our study suggests that cardiac catheterization, predominantly intervention, is associated with myocardial injury, even in the absence of complications.