The Minnesota Heart Survey (MHS) assessed population trends in coronary heart disease (CHD) mortality, morbidity and risk factor levels in the Twin Cities metropolitan area to explain the decline in CHD deaths. Age-adjusted CHD mortality rates declined in Twin Cities residents aged 30 to 74 from 1968 to 1986 by 52% in men and 58% in women. Much of the decline in CHD mortality was attributable to decreased out-of-hospital deaths. Attack rates based on hospitalized definite myocardial infarction (MI) did not change from 1970 to 1985, and hospital case-fatality rates declined consistently from 1970 to 1985 (from 21% to 11% in men, from 27% to 17% in women). Dramatic increases were noted in the percentage of patients undergoing cardiac procedures (coronary artery bypass, angioplasty, and thrombolytic agents). Trends in CHD rates were associated with improved population levels of risk factors. Average serum total cholesterol levels decreased by 8 mg/dl and 11 mg/dl between 1973 and 1987 in men and women, respectively. Cigarette smoking prevalence declined from approximately 40% to 30%. Average systolic blood pressure apparently declined about 1 mm Hg and diastolic blood pressure by 2 mm Hg from 1973 to 1987. Body mass index (wt/ht2) increased by 1 unit in men and 1.7 units in women from 1973 to 1987. These data suggest that a combination of primary prevention and improved medical care of acute CHD contributed to the decline in CHD mortality.