Dr. Marx has been caring for patients with congenital heart disease since beginning his cardiology fellowship in 1979. This has included the diagnosis and medical and surgical planning and care of the fetus and newborn. He has followed those patients, and evaluated new patients through infancy, childhood, adolescence and adulthood. In addition, Dr. Marx has concentrated on non-invasive imaging, in particular, the application of two and three –dimensional imaging to the care of his patients. He has also focused on the analysis and care of patients with valve abnormalities, in particular the Cone operation for Epstein’s disease, and on care of patients with aortic and mitral valve disease. Dr. Marx is also a member of the Boston Children’s Hospital committee on bi-ventricular repairs. This group is involved in the selection and medical and surgical treatment and analysis of the outcomes of “bi-ventricular surgery.” His particular research has evolved around the application of echocardiography, in particular three-dimensional echocardiography to improve the diagnosis and care of patients with congenital heart disease. This includes evaluating the outcome of specific surgical procedures such as valve repairs and bi-ventricular surgeries.