Chronic heart failure (CHF) is an increasingly common cardiovascular disorder. Many patients who have CHF report moderate to marked decreases in the frequency of sexual activity, and up to 75% of patients report erectile dysfunction (ED). There are few controlled clinical data on the efficacy and safety of sildenafil citrate in men who have ED and CHF; thus, we evaluated these parameters in patients who had stable CHF. This was a double-blind, placebo-controlled, flexible-dose study. Men who had ED and stable CHF were randomized to receive sildenafil or placebo for 12 weeks. Primary outcomes were questions 3 and 4 of the International Index of Erectile Function. Secondary outcomes included the 5 functional domains of the International Index of Erectile Function, 2 global efficacy assessment questions, intercourse success rate, the Erectile Dysfunction Inventory of Treatment Satisfaction, and the Life Satisfaction Checklist. By week 12, patients who received sildenafil (n = 60) showed significant improvements on questions 3 and 4 compared with patients who received placebo (n = 72; p <0.002). Larger percentages of patients who received sildenafil reported improved erections (74%) and improved intercourse (68%) compared with patients who received placebo (18% and 16%, respectively). Intercourse success rates were 53% among patients who received sildenafil and 20% among those who received placebo. Patients who received sildenafil were highly satisfied with treatment and their sexual life compared with patients who received placebo. Sixty percent of patients who received sildenafil and 48% of patients who received placebo developed adverse events, including transient headache, facial flushing, respiratory tract infection, and asthenia. The incidence of events related to cardiovascular effects was low. Sildenafil is an effective and well-tolerated management of ED in men who have mild to moderate CHF.