We evaluated predictive value of left ventricular ejection fraction at rest (REF) and its increment with exercise (deltaEF) on autologous and allogeneic stem cell transplantation mortality. In a 7 year period, a total of 163 patients evaluated for stem cell transplantation were studied. All were followed for at least 3 months after the transplant. REF was discriminatory for peritransplant mortality only in younger (<43 years) patients (n = 66), particularly those who underwent autologous transplantation (n = 30). Resting ejection fraction was not a discriminator for early death in any other subgroup. Cardiac reserve (deltaEF) was significantly lower in patients (n = 35), who died early. The finding was most prominent in younger patients who underwent autologous transplantation (n = 26). Combination of decreased REF and low deltaEF (n = 18) was associated with high peritransplant mortality (56%), after both autologous and allogeneic transplantation. A low REF with an appropriate deltaEF (n = 43) was associated with a 19% peritransplant mortality and no deaths in the autologous group. These observations indicate that resting ejection fraction is of only limited value for pretransplant evaluation. However, measurement of cardiac reserve during exercise can provide important prognostic information before stem cell transplantation.