Objectives. The purpose of this study was to test the hypothesis that active compression decompression would improve resuscitation success in human subjects after cardiac arrest. Background. Active compression decompression cardiopulmonary resuscitation is a new method that improves cardiopulmonary hemodynamic function in animal models and humans after cardiac arrest. Methods. We conducted a prospective randomized clinical trial in patients with in hospital cardiac arrest. Patients were assigned to receive standard manual or active compression-decompression cardiopulmonary resuscitation. The primary study end points were spontaneous return of circulation, 24-h survival and survival to hospital discharge. Results. Fifty-three consecutive patients after cardiac arrest undergoing 64 resuscitation attempts were studied (30 women, 23 men; mean [+/-SD] age 71 +/- 13 years, range 38 to 96). Spontaneous return of circulation was observed in 24 (47%) of 53 patients and was increased in patients receiving active compression-decompression compared with those receiving standard manual cardiopulmonary resuscitation (15 [60%] of 25 vs. 9 [32%] of 28, respectively, p = 0.042); 24-h survival was increased (12 [48%] of 25 vs. 6 [21%] of 28, respectively, p = 0.041); and there was a trend toward improved survival to hospital discharge (6 [24%] of 25 vs. 3 [11%] of 28, respectively, p = 0.198) when active compression decompression was compared with standard manual cardiopulmonary resuscitation. Conclusions. Active compression-decompression cardiopulmonary resuscitation improves return of spontaneous circulation and 24-h survival after in-hospital cardiac arrest. Active compression-decompression cardiopulmonary resuscitation appears to be a beneficial adjunct to standard manual cardiopulmonary resuscitation.