Social capital has been shown to be associated with reduced mortality due to cardiovascular disease. Our aim was to determine the association of time-varying community-level social capital (CSC) with recurrence of acute coronary syndrome using a retrospective cohort study design. A total of 34,752 men and women were identified, aged 30-85 years, who were hospitalized for acute coronary syndrome between January 1, 1998 and December 31, 2002 in Kaiser Permanente Northern California, USA, an integrated health care delivery system. The primary outcome was recurrent non-fatal or fatal acute coronary syndrome; median follow-up was 19 months. We estimated random-effects, three-level Cox proportional hazard models adjusting for sex, age, race/ethnicity, comorbidities, medication use, and revascularization procedures at level 1, median household income for the census block-group at level 2, and income inequality, racial/ethnic concentration, penetration of health maintenance organizations, and CSC at level 3. Our measure of CSC was the previously validated Petris Social Capital Index (PSCI). We found that a one-standard deviation increase in the PSCI, after adjusting for the above covariates, was significantly associated with decreased recurrence of acute coronary syndrome only for those living in areas where block-group level median household income was below the grand median compared to those living in areas where block-group level median household income was at the grand median or above. These results suggest that community-level social capital may be negatively associated with recurrence of acute coronary syndrome among lower-income individuals.