Summary:Cardiac complications may result from high-dose chemotherapy or irradiation administered during the conditioning phase of bone marrow and blood stem cell transplantation (BMT). To assess the frequency of clinically serious cardiac toxicity related to the acute phase of BMT, we retrospectively examined life-threatening or fatal cardiotoxicity identified using the complications records of our transplant center clinical database. All serious cardiac toxicity events within 100 days of BMT except those attributable to septic shock, pneumonitis or multi-organ failure were reviewed. Of 2821 BMT patients at the University of Minnesota between 1977 and 1997, 26 were identified as having suffered major or fatal (n = 13) cardiotoxicity (0.9%, 19 adults and seven children). Rapidly progressive heart failure resulted in death of 11 patients, one patient had fatal pericardial tamponade, and one had an acute ventricular fibrillation arrest. The remaining 13 patients (50%) had lifethreatening cardiotoxicity including four patients with pericardial tamponade and nine patients with cardiac arrhythmias. Overall, we observed that acute, major cardiotoxic events attributable to BMT are uncommon, occurring with a frequency of Ͻ1%. These data suggest that with appropriate pre-transplant clinical evaluation, high-dose cyclophosphamide and irradiation in the BMT preparative phase does not result in frequent, clinically relevant short-term cardiac toxicity. Bone Marrow Transplantation (2001) 28, 283-287.