Reduced-intensity conditioning (RIC) extends hematopoietic stem cell transplants (HSCT) to elderly or debilitated patients who are not candidates for HSCT. The incidence and outcomes of cardiac complications have been reported following myeloablative HSCT. We assessed the incidence and outcomes of cardiac complications in 278 recipients of RIC from July 2000 to July 2006. All patients received conditioning with BU, fludarabine and TBI. Patients were evaluated from conditioning therapy until 100 days after HSCT. Median age was 56 years. Cardiac events were defined as either one or more of the following: arrhythmias, myocardial infarction or congestive heart failure. Twenty-five patients developed arrhythmias at a median of 3 days post transplant, in 19 patients hemodynamic compromise occurred and mechanical ventilation was required in 15 patients. The arrhythmias included atrial fibrillation (n=17), atrial flutter (n=6) and supraventricular tachycardia (n=2). Troponin was elevated in 12 out of 25 patients. The mean brain natriuretic peptide was 679. All patients converted to a normal rhythm by medical therapy at a median of 2 days. Recurrence of arrhythmia occurred in 76% of patients. Day 100 mortality was 40% in this group. A history of high-dose anthracycline treatment and a low ejection fraction were risk factors for the development of cardiac complications.