Mortality rates from coronary heart disease (CHD), which had risen during the twentieth century in many countries, started declining in some countries during the 1960s. Once initial skepticism about the validity of the observed trends dissipated, researchers attempted to generate explanations about the events that had transpired using a variety of techniques, including ecological examinations of the trends in risk factors for CHD and changes in management of CHD, multivariate risk equations, and increasingly sophisticated modeling techniques. Improvements in risk factors as well as changes in cardiac treatments have both contributed to the reductions in CHD mortality, although estimates of their contributions have varied among countries. Models suggest that additional large reductions in CHD mortality are feasible by either improving the distribution of risk factors in the population or raising the percentage of patients receiving evidence-based treatments.