Intra-aortic balloon (IAB) counterpulsation has been utilized as an effective "bridge" to transplantation in patients with end-stage heart failure. To determine if patients with heart failure with nonischemic cardiomyopathy (NICM) derive the same benefit from IAB support as those with ischemic cardiomyopathy (ISCM), we evaluated 27 patients with NICM and 16 patients with ISCM who required IAB support while awaiting transplantation. Hemodynamic changes, effects on organ function (renal and hepatic), frequency of complications, and clinical outcomes were analyzed. Baseline demographics and hemodynamics were comparable in both groups (p = NS). Hemodynamics improved in both groups, immediately (15 to 30 min) following IAB insertion, with greater improvement (p < 0.05) in cardiac index and a trend toward greater reduction in filling pressures in the NICM group. Systemic vascular resistance fell to a similar degree in both groups. During continued IAB support (0.13 to 38 days in NICM, 1 to 54 days in ISCM), all hemodynamic changes persisted in both groups, with larger decrease (p < 0.05) in systemic vascular resistance and greater increase (p < 0.05) in cardiac index in the patients with NICM. The reduction in filling pressures, however, tended to be greater in patients with ISCM. Renal and hepatic function parameters improved to a similar extent in both groups. The frequency of complications and clinical outcome during IAB support were also similar in the two groups. These data confirm that IAB counterpulsation is a safe and effective "bridge" in patients with both NICM and ISCM with end-stage heart failure. The mechanism of sustained benefit in the two groups, however, may be different; afterload reduction appears to be more important in patients with NICM whereas reduction in filling pressures (increased coronary perfusion pressure) may be the main mechanism in patients with ISCM.