While strengthening primary care quality is key to China’s health system reforms, evidence to guide this work has been limited, particularly for rural areas. This study provides the first nationally-representative assessment of village doctors' competence in diagnosing and managing presumptive heart disease. Across-sectional study of village clinics was conducted across five provinces. We presented standardized clinical vignettes to evaluate clinicians' competence in diagnosing and managing unstable angina. Enumerators accompanying mock patients documented the interaction, including questions, physical examinations, diagnoses, and management options provided by the doctor. We measured diagnostic process competence as adherence to "recommended" questions and examinations based on national clinical practice guidelines, diagnostic competence according to whether clinicians provided a correct diagnosis, and management as correct medication and/or referral. Management was assessed twice: following clinicians' own diagnoses determined through questioning and examinations, and after enumerators provided doctors with the correct diagnosis. Clinicians completed 26% (95% CI 24% to 28%) of recommended diagnostic questions and examinations; 20% (14% to 27%) arrived at a correct diagnosis. Rates of correct management were 43% (35% to 51%) following clinicians' own diagnosis and 51% (43% to 59%) after being given the correct diagnosis. When given the correct diagnosis and only asked to provide treatment, clinicians prescribed 82% fewer potentially harmful medications than in treatments based on their own (potentially incorrect) diagnosis. The ability of village doctors to diagnose a textbook case of unstable angina is limited. Deficits in diagnostic competence led to low rates of correct management.