BACKGROUND: The determinants of depression following acute coronary syndrome (ACS) are poorly understood. Triggering of ACS by emotional stress and low socio-economic status (SES) are predictors of adverse outcomes. We therefore investigated whether emotional triggering and low SES predict depression and anxiety following ACS. METHOD: This prospective observational clinical cohort study involved 298 patients with clinically verified ACS. Emotional stress was assessed for the 2 h before symptom onset and compared with the equivalent period 24 h earlier using case-crossover methods. SES was defined by household income and education. Depression was measured with the Beck Depression Inventory and the Hamilton Rating Scale for Depression and anxiety with the Hospital Anxiety and Depression Scale 3 weeks after ACS and again at 6 and 12 months. Age, gender, ethnicity, marital status, the Global Registry of Acute Coronary Events risk score, duration of hospital stay and history of depression were included as covariates. RESULTS: Emotional stress during the 2-h hazard period was associated with increased risk of ACS (odds ratio 1.88, 95% confidence interval 1.01-3.61). Both low income and emotional triggering predicted depression and anxiety at 3 weeks and 6/12 months independently of covariates. The two factors interacted, with the greatest depression and anxiety in lower income patients who experienced acute emotional stress. Education was not related to depression. CONCLUSIONS: Patients who experience acute emotional stress during their ACS and are lower SES as defined by current affluence and access to resources are particularly vulnerable to subsequent depression and anxiety.