(a) female; (b) date of birth before January 1, 1955; (c) a reported history of myocardial infarction (MI), stroke (CVA), angina pectoris (AP), coronary artery bypass grafting (CABG), percutaneous transluminal angioplasty (PCTA), transient ischemic attack (TIA), carotid endarterectomy (CEA), or peripheral artery surgery (PAS); (d) no history of cancer (except non-melanoma skin cancer) within the past 10 years and no active liver disease or cirrhosis; (e) pregnancy physiologically impossible due to menopause (natural or surgical) or tubal ligation, or the participant does not intend to become pregnant in the future as indicated on the initial WHS questionnaire; (f) no current use of a vitamin K-depleting anticoagulant agent (e.g., Coumadin). Individuals taking aspirin or other NSAIDs were not excluded.