Wide variability in the antiplatelet effects of aspirin may lead to recurrent thromboembolic events. Several pilot studies have suggested potential benefits of taking aspirin at bedtime rather than in the morning. The primary objective of this study is to examine whether aspirin administration at bedtime versus in the morning provides a superior reduction in the incidence of major adverse cardiovascular events among patients with or without established atherosclerotic cardiovascular disease, who are already taking aspirin.