['Current evidence suggests the CD40-CD40L pathway as a key process in the development, progression, and outcome of acute coronary syndrome (ACS). The aim was to investigate the prognostic importance of soluble (s) CD40L levels, single nucleotide polymorphisms (SNP) in the CD40LG gene, and the relation between sCD40L and SNPs in patients with acute coronary syndromes (ACS).', 'Samples were obtained on admission from 2359 patients with non-ST elevation ACS randomized to an early invasive versus a conservative and to placebo controlled long-term dalteparin treatment in the FRISC-II study. The -3459 A>G SNP was identified as a novel regulator of sCD40L levels (P = 0.001). In the placebo-treated group, sCD40L levels above median were associated with a 2.5-fold increased risk of myocardial infarction (MI) (P < or = 0.001) but not with raised mortality. In the dalteparin treated group, sCD40L showed no association with MI (P = 0.75). Consequently, dalteparin treatment was effective in reducing the risk of MI only in patients with sCD40L levels above median. A combined assessment of troponin-T and sCD40L complemented the prognostic information on risk of MI.'] Are soluble CD40L levels regulated by the -3459 A > G polymorphism and predict myocardial infarction and the efficacy of antithrombotic treatment in non-ST elevation acute coronary syndrome?