The prognosis of patients with coronary heart disease is closely related to the degree of coronary luminal obstruction. In population studies, the incidence and severity of coronary atherosclerosis on angiography is correlated with diet and plasma lipoprotein cholesterol. Previous clinical trials had shown that treatments that lowered plasma concentrations of low density lipoprotein cholesterol benefited some hypercholesterolemic patients with coronary heart disease. No similar benefit had been demonstrated in normocholesterolemic patients who make up the majority of patients with coronary heart disease.