National guidelines recommend a team model of care to facilitate adherence to evidence-based practices; however, previous studies suggesting benefit may have limited generalizability. The aim of this study was to examine the influence of advanced practice nurse (APN) and physician assistant (PA) staffing on the delivery of guideline-recommended therapies for outpatients with heart failure (HF). The Registry to Improve the Use of Evidence-Based Heart Failure Therapies in the Outpatient Setting (IMPROVE HF), a prospective cohort study, enrolled 167 cardiology practices to characterize outpatient management of 15,381 patients with chronic HF and left ventricular ejection fractions < or =35%. Adherence to guideline-recommended HF therapies was recorded, and the presence of APN and PA staffing was assessed by survey. Multivariate models identified contributions to the delivery of guideline-recommended HF therapies. Of cardiology outpatient practices, 66.0% had APNs and PAs. Practices with 0, >0 to <2, and > or =2.0 APN and PA staffing had similar adherence to the 7 guideline-recommended HF therapies. After adjustment, staffing with > or =2 APNs or PAs was associated with greater conformity with 2 of 7 measures (implantable cardioverter-defibrillator therapy and delivery of HF education, p < or =0.01 for both) and similar conformity to angiotensin-converting enzyme inhibitor or angiotensin receptor blocker therapy, beta-blocker therapy, aldosterone antagonist therapy, anticoagulation for atrial fibrillation, and cardiac resynchronization therapy. In conclusion, staffing with APNs and PAs varied in cardiology outpatient practices. Compared to no APNs or PAs, > or =2.0 APNs or PAs per cardiology practice was associated with the greater use of implantable cardioverter-defibrillator therapy and delivery of HF education and equivalent use of drug and cardiac resynchronization therapies.