A case control study will be carried out to evaluate whether the long-term use of oral contraceptives (OCs), after discontinuation, is associated with an increased incidence of first nonfatal myocardial infarction (MI) among women above the age of 50 years and younger women. While it is known that current OC use (use in the preceding month) increases the risk of MI some three to four-fold, recent evidence raises the hypothesis that past use that lasted a total of five or more years is associated with a residual two-fold increase in MI risk among women 40 to 49 years old. Since the incidence of the disease starts to become appreciable beyond age 49, it is of public health importance to reexamine this hypothesis in a data base that includes women aged 50 or older, to determine how long the increased risk, if any, persists, and to determine whether it varies according to the formulation of the preparation used. An increase in risk that persists after discontinuation of OC use would have major public health implications, since millions of women have used or will use OCs for long periods: in our data, about 5% of women in their 50s, over 10% of women aged 40-49, and over 15% of women under age 40 have already used OCs for at least five years. Moreover, many of the OCs used in the past are still commonly used today. The study will also enable evaluation of the effects on MI risk of current OC use, machine-determined levels of carbon monoxide and nicotine in cigarettes, noncontraceptive estrogens, and other potential risk factors. The study will be carried out in 78 hospitals located in greater Boston, southern Connecticut, and Westchester County, a network recently used for a study of MI in young men. The study will be contined to women 57 years of age or younger because the rate of past long-term OC use is very low beyond that age. Cases will be identified by weekly telephone calls to the coronary care units. Nurse-interviewers will be dispatched to the hospitals to administer standard interviews to cases convalescing on medical wards after discharge from the coronary care units, and to controls identified in the same hospitals. Histories of OC use, including the timing and duration of use and the name of the preparations, will be recorded along with information on other drug use, descriptive factors, and MI risk factors that might be confounding variables or that might modify the effect of OCs (e.g. cigarette smoking). The data collection will last three years, and a total of about 900 cases of first infarction and about 3600 controls, approximately frequency matched for age to the cases, will be studied.