Background - Prior investigations suggest that superimposing continuous flow on aortic flow (continuous aortic flow augmentation) produces vasodilation, cardiac unloading, and improved cardiac performance. Methods and Results - We compared percutaneous continuous aortic flow augmentation (flow ≤ 1.5 L/min for up to 96 hours) plus medical therapy versus medical therapy alone by randomizing 168 patients (device, n = 109; control, n = 59) hospitalized with heart failure, reduced left ventricular ejection fraction and cardiac index, elevated pulmonary capillary wedge pressure, and renal impairment or substantial diuretic requirement despite intravenous inotropes/vasodilators. The primary composite efficacy end point included pulmonary capillary wedge pressure (72 to 96 hours) and days alive out of hospital off mechanical support over 35 days. The population's illness severity posed unique challenges. Enrollment ended early because of an inability to demonstrate significant benefit on the primary composite end point (device, 17.4%; control, 13.6%; P=0.45) in the face of excess device group bleeding. Pulmonary capillary wedge pressure decreased from 28.8±6.3 mm Hg (mean±SD) to 24.9±7.2 mm Hg (average, 72 to 96 hours) and 28.9±7.1 to 26.5±6.2 mm Hg in the device and control groups, respectively (between-group P=0.074). Cardiac index progressively increased in the device (2.05±0.53 to 2.44±0.52 L·min -1·;m-2) but not the control (between-group P<0.0001) group. Thirty-five-day Kansas City Cardiomyopathy Questionnaire Overall Summary scores increased by 38.4±22.7 and 31.2±26.0 points in the device and control groups (between-group P=0.10). Through 65 days, device-to-control hazard ratios were as follows: all-cause mortality, 1.05 (95% confidence interval, 0.60 to 1.82); death or heart failure hospitalization, 0.87 (95% confidence interval, 0.57 to 1.33); and heart failure hospitalization, 0.66 (95% confidence interval, 0.38 to 1.13). Major bleeds occurred in 16.5% in the device (7.3% treatment related) and 5.1% in the control (P=0.05) group. Conclusions - Continuous aortic flow augmentation improved cardiac performance, improving cardiac index and pulmonary capillary wedge pressure, but statistical significance for the primary efficacy end point was not attained. Hemodynamic and clinical observations provide direction toward additional studies to further investigate the clinical effects of this treatment. © 2008 American Heart Association, Inc.