Objectives: The goal of this study was to determine whether there are differences in populations of patients with heart failure who require univentricular or biventricular circulatory support. Methods: Two hundred thirteen patients who were in imminent risk of dying before donor heart procurement and who received Thoratec left (LVAD) and right (RVAD) ventricular assist devices at 35 hospitals were divided into three groups: group 1 (n = 74), patients adequately supported with isolated LVADs; group 2 (n = 37), patients initially receiving an LVAD and later requiring an RVAD; and group 3 (n = 102), patients who received biventricular assistance (BiVAD) from the beginning. Results: There were no significant differences in any preoperative factors between the two BiVAD groups. In the combined BiVAD groups, pre-VAD cardiac index (BiVAD, 1.4 ± 0.6 L/min per square meter, vs LVAD, 1.6 ± 0.6 L/min per square meter) and pulmonary capillary wedge pressure (BiVAD, 27 ± 8 mm Hg, vs LVAD, 30 ± 8 mm Hg) were significantly lower than those in the LVAD group, and pre-VAD creatinine levels were significantly higher (BiVAD, 1.9 ± 1.1 mg/dl, vs LVAD, 1.4 ± 0.6 mg/dl). In addition, greater proportions of patients in the BiVAD groups required mechanical ventilation before VAD placement (60% vs 35%) and were implanted under emergency conditions than in the LVAD group (22% vs 9%). The survival of patients through heart transplantation was significantly better in patients who had an LVAD (74%) than in those who had BiVADs (58%). However, there were no significant differences in posttransplantation survival through hospital discharge (LVAI), 89%; BiVAD, 81%). Conclusion: Patients who received LVADs were less severely ill before the operation and consequently were more likely to survive after the operation. As the severity of illness increases, patients are more likely to require biventricular support.