['Depression and anxiety are linked to coronary events but the mechanism(s) remains unclear. We investigated the associations of depression and anxiety with serotonin-mediated platelet hyperactivity in coronary artery disease (CAD) patients in a cross-sectional study.', 'Three months after an acute coronary event, stable CAD patients (n = 83) on aspirin and clopidogrel were evaluated for depression (beck depression inventory) and anxiety (hospital anxiety and depression scale), and their platelet reactivity was measured (optical aggregometry and flow cytometric fibrinogen binding in response to adenosine diphosphate (ADP = 5 microM) and two serotonin + epinephrine doses [5HT:E (L) = 4 microM + 4 microM and 5HT:E (H) = 10 microM + 4 microM]. Platelet reactivity was significantly higher in depressed and anxious than in depressed only or non-depressed-and-non-anxious patients. Aggregation (mean +/- SE) was 41.9 +/- 2.6% vs. 32.2 +/- 2.6% vs. 30.4 +/- 3.7% with 5HT:E (L) and 46.9 +/- 2.7% vs. 35.6 +/- 2.7% vs. 31.7 +/- 3.8% with 5HT:E (H) (P < 0.05 for both). Differences in ADP aggregations were not significant, perhaps because of clopidogrel therapy. Flow cytometry findings were similar. In a multivariate linear regression model adjusted for age, body mass index, and each other, anxiety symptoms independently predicted all 5HT:E-mediated platelet reactivity measures, whereas depression predicted none.'] Is anxiety a better predictor of platelet reactivity in coronary artery disease patients than depression?