Purpose: To improve cardiovascular care through supporting primary care practices' adoption of evidence-based guidelines. Study Design: A cluster randomized trial compared two approaches: (1) standard practice support (practice facilitation, practice assessment with feedback, health information technology assistance, and collaborative learning sessions) and (2) standard support plus patient engagement support. Methods: Primary outcomes were cardiovascular clinical quality measures (CQMs) collected at baseline, 9 months, and 15 months. Implementation of the first 6 "Building Blocks of High-Performing Primary Care" was assessed by practice facilitators at baseline and 3, 6, and 9 months. CQMs from practices not involved in the study served as an external comparison. Results: A total of 211 practices completed baseline surveys. There were no differences by study arm (odds ratio [95% confidence interval]) for aspirin use (1.03 [0.99, 1.06]), blood pressure (0.98 [0.95, 1.01]), cholesterol (0.96 [0.92, 1.00]), and smoking (1.01 [0.96, 1.07]); however, there were significant improvements over time in aspirin use (1.04 [1.01, 1.07]), cholesterol (1.05 [1.03, 1.08]), and smoking (1.03 [1.01, 1.06]), but not blood pressure (1.01 [0.998, 1.03]). Improvement in enrolled practices was greater than external comparison practices across all 4 measures (all P < .05). Implementation improved in both arms for Team-Based Care, Patient-Team Partnership, and Population Management, and improvement was greater in enhanced intervention practices (all P < .05). Leadership and Data-Driven Improvement (P < .05) improved significantly, with no difference by arm. A greater improvement in Building Block implementation was associated with a greater improvement in blood pressure measures (P < .05). Conclusions: Practice transformation support can assist practices with improving quality of care. Patient engagement in practice transformation can further enhance practices' implementation of aspects of new models of care.