There are no well-controlled prospective clinical trials that provide evidence of the benefit of any particular medication in feline heart disease. This prospective blinded clinical trial compared the angiotensin-converting enzyme inhibitor benazepril (mean dosage, 0.7 mg/kg once daily; range, 0.5-1.0 mg/kg once daily) with placebo given once daily for up to 2 years. Client-owned cats (n = 151) with confirmed heart disease of various etiologies with or without clinical signs of congestive heart failure were included. Benazepril was found to be well-tolerated; however, no significant differences in time to treatment failure, quality-of-life scores, or echocardiographic measurements were identified between the groups. However, because there were several important limitations of this study, no widespread conclusions should be made regarding potential treatment benefits.