Bernard Lown (June 7, 1921 – February 16, 2021) was a Lithuanian-American cardiologist and inventor. Lown was the original developer of the direct current defibrillator for cardiac resuscitation, and the cardioverter for correcting rapid disordered heart rhythms. He introduced a new use for the drug lidocaine to control heartbeat disturbances.

Throughout his medical career, Lown focused on two major medical challenges: the problem of sudden cardiac death and the role of psychological stress on the cardiovascular system. His investigations led to many medical break-throughs, among them the coronary care unit. His work made possible and safe much of modern cardiac surgery, as well as a host of other innovations. In 1985, Lown accepted the Nobel Peace Prize on behalf of the International Physicians for the Prevention of Nuclear War, an organization he co-founded with Soviet cardiologist Yevgeny Chazov, who later was Minister Of Health of the USSR.

Lown was Professor of Cardiology Emeritus at the Harvard T.H. Chan School of Public Health, and Senior Physician Emeritus at the Brigham and Women’s Hospital, Boston, Massachusetts. He was the founder of the Lown Cardiovascular Center and Lown Cardiovascular Research Foundation. He also founded the Lown Institute, which aims to reform both the healthcare system and society.

Lown was born in Utena, Lithuania as Boruch Lac, on June 7, 1921, the son of Nison and Bela (Grossbard) Lac. His family was Jewish, and one of his grandfathers was a rabbi. They emigrated to Maine when Lown was 14, and he attended Lewiston High School, graduating in 1938.

Lown went on to study zoology at the University of Maine, obtaining a bachelor's degree from that institution in 1942. He subsequently earned an M.D. from Johns Hopkins University School of Medicine in 1945. His medical training included Yale-New Haven Hospital (Yale University, New Haven, Connecticut); Montefiore Medical Center, Bronx, NY; and a cardiology fellowship at the Peter Bent Brigham Hospital (now Brigham and Women’s Hospital, in Boston). His mentor in cardiology was the renowned clinical cardiologist Samuel A. Levine.

Lown helped raise international medical awareness of sudden cardiac death as a leading cause of mortality in the developed world. Based on patient observations, Lown concluded that sudden cardiac death was reversible and survivable, and that people who were successfully resuscitated could have a near normal life expectancy.

Working with his mentor Samuel A. Levine, Lown realized that the high mortality of a heart attack, then 35 percent, was most likely due to a strict regimen of bed rest. Patients remained completely recumbent for six or more weeks. A major complication of bed rest was pulmonary embolism, which accounted for a significant part of the mortality. Although Lown encountered enormous opposition and hostility among doctors to the so-called "chair treatment", in 81 patients so treated, mortality was reduced by two thirds. Once the work was published, the chair treatment was rapidly adopted and hospitalizations were reduced to several days. Untold lives were saved by getting patients out of bed.

Until the 1950s, ventricular fibrillation of the heart was treated with drug therapy alone. In 1956 American cardiologist Paul Zoll described resuscitations during open-heart surgery and, later after sudden cardiac death, by means of an alternating current (AC) electric shock, derived from a wall socket. AC current was untested as to its safety and efficacy and could cause death. In 1959, Lown demonstrated that AC was injurious to the heart and could be lethal. These investigations were conducted in the Department of Nutrition at the Harvard School of Public Health. The work was supported by Professor Frederick Stare, chairman of the Department of Nutrition.