This proposal describes a five-year training program for the development of an academic career in Cardiology. The principle investigator obtained his MD/PhD from Stanford School of Medicine and has completed clinical training in Internal Medicine, Cardiology, and Interventional Cardiology at Massachusetts General Hospital (MGH). He will now focus on the study of stem cell and developmental biology as it pertains to cardiac disease under the mentorship of Dr. Kenneth Chien. Dr. Chien, a leader in the field of cardiac development, is chief of the Cardiovascular Research Center (CVRC) at the MGH and Leader of the Cardiovascular Disease Program at the Harvard Stem Cell Institute (HSCI). He has trained numerous physician scientists. To promote training in stem cell biology, the principle investigator has already spent one year training withDr. Stuart Orkin, a pioneer in stem cell biology. Dr. Orkin will continue to play a prominent role in training the principle investigator as an Advisory Committee member. In addition, Dr. Kenneth Bloch and Dr. Randall Peterson, both recognized leaders in cardiovascular biology, will serve mentorship roles on the Advisory Committee. The CVRC and the HSCI provide an ideal setting for training physician- scientists in the rapidly converging areas of cardiac development and stem cell biology. The research program will focus on lineage commitment and differentiation during murine cardiac development. Acquired and congenital heart disease represents a leading cause of mortality and morbidity in the world and many of the genes important in cardiac development have been implicated in human congenital heart disease. Defining the molecular pathways that