On-going studies of hormone-replacement therapy in women at Group Health Cooperative of Puget Sound (GHC) identified all female enrollees who suffered a first heart attack since 1986; the study expanded this inception cohort through 1996. Information from medical record review and GHC databases were used to assess risk factors and co-morbid conditions, both at entry into the cohort and up to ten years of follow-up, and to identify recurrent cardiovascular events and deaths. A complete record of prescription drug exposure during the follow-up period was obtained for each subject from the GHC computerized pharmacy database. Although the main hypothesis related to reinfarction risk in women, men were studied as well to facilitate comparison of the results of this observational study with those of the clinical trials. According to conservative estimates of the available sample size, the investigators had 86 percent power to detect a relative risk of 1.45 in women alone, and 85 percent power to detect a relative risk of 1.25 in men and women combined, for the association of calcium-channel blocker use with fatal or non-fatal reinfarction. The study also examined the safety and efficacy of other cardiovascular drugs commonly used in women after myocardial infarction, including angiotensin converting-enzyme inhibitors, lipid-lowering drugs, and estrogen replacement therapy.