Because of a perceived linear relationship between blood pressure and mortality, the body of epidemiologic data has been used to support the concept that the lower the blood pressure, the better off the patient will be. However these data are flawed by the fact that casual blood pressures in untreated, nonhypersensives were used. No treatment data exist to support lowering diastolic blood pressure to less than 85 mmHg; new information indicates that diastolic blood pressures less than 85 mmHg may be associated with an increase in coronary heart disease (CHD) mortality. This has been called the J-curve theory, to describe the shape of the relationship evidence suggests that the J-curve effect may have an association with pre-existing cardiovascular disease. While it is important to treat patients aggressively to reduce an elevated blood pressure, a decrease in the diastolic pressure to less than 85 mmHg may impair diastolic myocardial perusion pressure in susceptible patients. The target diastolic blood pressure in most studies has been less than 90 mmHg, and this is the treatment goal recommended by the Joint National Committee Guidelines. Until definitive evidence of the J-curve relationship is available from the ongoing clinical trials, it may be prudent, particularly in those patients with pre-existing cardiovascular disease, to avoid excessive lowering of diastolic blood pressure.