Background: The Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) is an NIH-sponsored registry of US FDA-approved mechanical circulatory support devices (MCSDs) used for destination therapy, bridge to transplantation (BTT), or recovery of the heart. INTERMACS data were analyzed through the most recent quarter ending March 31, 2008. Study Design: INTERMACS variables include demographics, patient outcomes (survival and adverse events), hemodynamic data, and laboratory values. Data were analyzed with competing outcomes methods. Risk factors were identified for death and transplantation. Results: Ninety-four sites have prospectively enrolled 483 patients in INTERMACS (BTT, 80%; destination therapy, 15%; bridge to recovery, 5%). Forty-two percent of patients had critical cardiogenic shock before implantation, 38% had progressive circulatory decline despite inotropic agents, and 8% were stable but inotropic agent-dependent. The remaining 12% had recurrent advanced heart failure, severe exercise intolerance, or advanced class III heart failure. At 6 months postimplantation, the competing outcomes for the 483 patients included ongoing support (42%), cardiac transplantation (33%), cardiac recovery with pump removal (3%), or death (22%). The most common causes of death were central nervous system events (11%), cardiovascular failure (8%), or respiratory failure (8%). Less common causes were infection (4%), device malfunction (4%), and liver failure (3%). Survival for BTT and destination therapy were similar (p = 0.53). Patient profile at the time of implantation (critical cardiogenic shock versus others) influenced survival (p = 0.007), as did device configuration (left ventricular assist device versus biventricular ventricular assist device; p < 0.0001). Conclusions: INTERMACS has increasing participation among domestic MCSD centers. The influence of preimplantation patient condition on survival underscores the importance of timely referral before critical cardiogenic shock occurs. As more devices achieve US FDA approval, INTERMACS will become useful for comparing MCSDs. © 2009 American College of Surgeons.