Cardiac-output response to exercise was evaluated over a 2-year period in hematopoietic stem cell transplant recipients treated with cardiotoxic drugs. During the study period, resting cardiac function was normal; however, the cardiac output response to exercise decreased, and an association with exercise tolerance was observed. Regular assessments of cardiopulmonary function and exercise guidance are vital for patients at high risk of cancer therapy-related cardiac dysfunction, in line with the principles of cardiac oncology rehabilitation.