“It is outstanding news,” said Dr. Mark Creager, president of the American Heart Association and director of the Heart and Vascular Center at Dartmouth-Hitchcock Medical Center, who was not involved in the study. “It will serve as a road map and will save a significant amount of lives.”

If guidelines are changed because of this study — as blood pressure experts expect that they will be — an already falling death rate from heart attacks and stroke could drop even more, said Dr. Jackson T. Wright Jr., a blood pressure expert at Case Western Reserve University and University Hospitals Case Medical Center, and a study investigator. Because cardiovascular disease is still the leading cause of death in the United States, a change in blood pressure goals could also reduce the nation’s overall mortality rate, he said.

The study ventured into unknown territory that some had found a bit frightening. A systolic pressure that is naturally 120 might be good, but it is quite another matter to artificially drag pressure down so low with drugs.

Reaching a target that low would mean giving people more and more medications, and the side effects could cancel any benefit. Older people might be especially vulnerable to ill effects of a much lower blood pressure since many already take an array of drugs for chronic conditions, which might interact. A very low blood pressure could lead to dizziness and falls. Twenty-eight percent of the subjects in the new study were over age 75.

Less than two years ago, a National Heart, Lung and Blood Institute panel went in the opposite direction. People had been told to aim for a systolic blood pressure of 140. But the panel recommended a goal of 150 for people ages 60 and older, arguing that there were no convincing data showing lower is better.

Until now, many blood pressure experts thought they were doing about as well as possible. The incidence of strokes — the major consequence of high blood pressure — has fallen by 70 percent since 1972. The main problem was that so many patients with high blood pressure did not take their medications or took drugs that were not powerful enough.