This is an open label trial in which letermovir will be given as prophylaxis for the
prevention of CMV infection and disease to all heart transplants who are at risk for
cytomegalovirus. The study will compare a 30 patient prospective cohort to a retrospective
cohort of 374 heart transplant recipients for the rates of neutropenia. In addition, the
tolerability of letermovir will be assessed in this population.