BACKGROUND: Compared with white patients, black patients are more likely to undergo cardiac surgery at low-quality hospitals, even when they live closer to high-quality ones. Opportunities for organizational interventions to alleviate this problem remain elusive. OBJECTIVES: To explore physician isolation in communities with high proportions of black residents as a factor contributing to racial disparities in access to high-quality hospitals for cardiac surgery. RESEARCH DESIGN: Using national Medicare data (2008-2011), we mapped physician social networks at hospitals where coronary artery bypass grafting procedures were performed, measuring their degree of connectedness. We then fitted a series of multivariate regression models to examine for associations between physician connectedness and the proportion of black residents in the hospital service area (HSA) served by each network. MEASURES: Measures of physician connectedness (ie, repeat-tie fraction, clustering, and number of external ties). RESULTS: After accounting for regional differences in healthcare capacity, the social networks of physicians practicing in areas with more black residents varied in many important respects from those of HSAs with fewer black residents. Physicians serving HSAs with many black residents had a smaller number of repeated interactions with each other than those in other HSAs (P<0.001). When these physicians did interact, they tended to assemble in smaller groups of highly interconnected colleagues (P<0.001). They also had fewer interactions with physicians outside their immediate geographic area (P=0.048). CONCLUSIONS: Physicians in HSAs with many black residents are more isolated than those in HSAs with fewer black residents. This isolation may negatively impact on care coordination and information sharing. As such, planned delivery system reforms that encourage minorities to seek care within their established local networks may further exacerbate existing surgical disparities.