Congenital heart defects are the most common birth defects and represent an increasing proportion of adolescent and adult patients followed by cardiologists. While many of these patients have undergone successful palliative or corrective surgery with excellent functional results, most of them still require careful follow-up. Further, even complex lesions may first be diagnosed in adolescence and adulthood. Therefore, cardiologists caring for adults need to become more familiar with these defects. Assessment of the patient with known or suspected congenital heart defects requires a careful history, physical examination, and noninvasive assessment. In addition, the catheterization laboratory remains a critical venue for diagnosis and, increasingly, therapy. Pressure measurements, oximetry, and angiography remain cornerstones of diagnosis in selected patients and a variety of interventional procedures have become viable therapeutic alternatives in both pre- and postoperative patients.