The decline in coronary heart disease mortality in the United States may be due to decreasing incidence of clinically apparent coronary heart disease or increasing survival from its first clinical appearance or both. Prior to 1987, few data were available to confirm either one directly. However, increased risk, decreased medical care, or both may predispose the Mexican-American population to increased recurrence of myocardial infarction and decreased post myocardial infarction survival, and an overall greater mortality among survivors of myocardial infarction, than are observed for Anglos in the same community setting. The significance of the potential results lies most importantly in the following aspects of this research: estimation of the community-based incidence of hospitalization for suspect, definite or possible myocardial infarction; precise determination of recurrence rates and survival curves after myocardial infarction in community-wide hospital-based cohorts; analysis of the relation of the above to risk status as ascertained at hospitalization and to health care and preventive practices assessed periodically post-myocardial infarction; and comparison of these observations between Anglos and Mexican-Americans, a group of special interest and concern because of expected differences in natural history of coronary heart disease and near total lack of the relevant data.