We sought to characterize the frequency, severity, and attributability of adverse events (AE) in congenital cardiac catheterization and identify patient and procedural characteristics associated with AE. Risk for any AE was associated with age < 1 year (odds ratio [OR] 2.3), interventional cases (OR 2.2), increasing procedure type risk group (OR 1, 2.0, 2.5), and indicator of hemodynamic vulnerability (OR 1.6), all p < 0.001. Each of these and weight were also associated with increased risk for high severity events, except for young age. Our understanding of populations at risk for adverse outcomes in congenital cardiac catheterization cases can be enhanced through the development and refinement of variables that categorize procedure types and patient characteristics by similar risk for adverse outcomes.