HeartMasters Medical Associates Clinton Office: 7700 Old Branch Ave, Suite B-205, Clinton, MD 20735 | Phone: (301) 877-4933 | Fax: (301) 877-6963 Washington Office: 1647 Benning Rd. NE, Suite 103, Washington, DC 20002 | Phone: (202) 399-0133 | Fax: (202) 339-0132.