The Heart Failure Adherence and Retention Trial (HART) provided an opportunity to determine adherence to evidence-based guidelines (EBG) in patients with heart failure (HF). Ten hospitals were the source of 692 patients with HF (EF < 40%). Physicians of patients with HF were classified as adherent to EBG if the patient chart audit showed they were on a beta-blocker, ACE-inhibitor (ACE-I), or angiotensin receptor blocker (ARB). Patients were classified as adherent to EBG if MEMS pill caps were used appropriately more than 80% of the time. Sixty-three percent of physicians prescribed evidence-based medications that were adherent to clinical practice guidelines. New York Heart Association (NYHA) III patients were less likely to be adherent (P < 0.001), as were those with renal disease (P < 0.001) and asthmatics (P < 0.001). Nonadherent physicians were less likely to treat patients with beta-blockers (39% vs 98%, P < 0.001) and ACE-I or ARBs (71% vs 98%P < 0.001). Thirty-seven percent of patients prescribed evidence-based therapy failed to use the MEMS pill cap bottles appropriately and were more likely a minority or higher NYHA class. Adherence to evidence-based therapy is less than optimal in HF patients based on a combination of both physician and patient nonadherence. ©2011 Wiley Periodicals, Inc.