BACKGROUND: The first Sibrafiban Versus Aspirin to Yield Maximum Protection From Ischemic Heart Events Post-Acute Coronary Syndromes (SYMPHONY) trial showed no benefit of 2 doses of sibrafiban over aspirin for secondary prevention after acute coronary syndromes. In 2nd SYMPHONY, we compared low-dose sibrafiban plus aspirin (LDS+A), high-dose sibrafiban (HDS), and aspirin alone. METHODS AND RESULTS: When the first SYMPHONY results became known, enrollment in 2nd SYMPHONY was stopped prematurely at 6671 patients who had been treated for a median of 90 days. The primary end point of death, myocardial (re)infarction (MI), or severe recurrent ischemia did not differ significantly between aspirin (9.3%) and LDS+A (9.2%; OR, 0.98; 95% CI, 0.80 to 1.20) or HDS (10.5%; OR, 1.14; 95% CI, 0.9 to 1.39) patients. Secondary end points did not differ significantly between aspirin and LDS+A patients. Death or MI occurred significantly more often with HDS (OR, 1.43; 95% CI, 1.14 to 1.80), as did mortality alone (OR, 1.83; 95% CI, 1.17 to 2.88) and MI (OR, 1.32; 95% CI, 1.03 to 1.69). Major bleeding was significantly more frequent in LDS+A patients (5.7%) versus aspirin alone (4.0%) but not in HDS patients (4.6%). CONCLUSIONS: Combining aspirin with LDS did not improve outcomes after acute coronary syndromes and caused more bleeding compared with aspirin alone. There was a trend toward increased mortality in this group and a significant increase in the high-dose arm.