Dr. Hajjar was recruited from Massachusetts General Hospital and Harvard Medical School to head the Cardiovascular Research Center at Mount Sinai School of Medicine.

Prior to coming to Mount Sinai, Dr. Hajjar was an Associate Professor of Medicine at Harvard Medical School and Staff Cardiologist in the Heart Failure & Cardiac Transplantation Center at Massachusetts General Hospital. He was the director of the Cardiology Laboratory of Integrative Physiology & Imaging at Massachusetts General Hospital. He received his medical degree from Harvard Medical School and trained in Internal Medicine and Cardiology at Massachusetts General Hospital in Boston.