Lown was the original developer of the direct current defibrillator for cardiac resuscitation, and the cardioverter for correcting rapid disordered heart rhythms.

In 1985, Lown accepted the Nobel Peace Prize[2] 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.

[8] 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.

[8] 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.

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.

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.

To find a safer method of cardiac resuscitation, Lown enlisted the help of Baruch Berkowitz, an electrical engineer employed by American Optical Company (AO).

Alternating current caused burns in skeletal and heart muscle and induced atrial as well as ventricular fibrillation in a large majority of the animal experiments.

[13] He discovered that timing the electrical discharge outside the heart’s brief vulnerable period of 0.03 seconds in duration prevented ventricular fibrillation or sudden cardiac death.

The cardioverter and DC defibrillator were especially valuable in coronary care units, when patients are hospitalized when most susceptible to sudden cardiac death and other potentially malignant arrhythmias.

[14] In addition to advancing medical technology, Lown discovered new applications for two drugs that were widely used for cardiac problems: digitalis and lidocaine.

During a medical residency at the Montefiore Hospital in New York City, Lown demonstrated the critical role of potassium in determining the safe use of digitalis.

[16] In 1957, Lown was concerned with how to visualize an atherosclerotic aortic plaque occurring in the big coronary vessels that supply nutrients to the heart muscle.

Lown's work did show that, with fiber optics, it was possible to measure oxygen saturation in dogs, and determine the cardiac output in humans.

[17] Paradoxically, when Lown submitted two abstracts to the World Cardiology Conference in Mexico in 1964, one on the defibrillator and cardioversion, and one dealing with fiber optics, the former was rejected and the latter accepted.

In early 1961, Lown called together a group of physicians from Boston’s teaching hospitals to address the mounting threat of nuclear war between the USSR and the USA.

[18] By the end of 1961, the group had drafted five research articles about the medical consequences of a ten-megaton nuclear attack on the city of Boston, a magnitude considered both possible and likely by the U.S. military.

[20] In 1980, Lown called on a small number of doctors to organize against the mounting nuclear threat that followed USSR's invasion of Afghanistan and the election of the Reagan administration.

Among the American participants were astrophysicist and science populizer Carl Sagan; Admiral Noel Gayler, formerly head of the American Pacific Fleet, Director of the National Security Agency, and in charge of targeting nuclear weapons against he USSR; Howard Hiatt, Dean of the Harvard School of Public Health; and Herbert Abrams, head of Radiology at the Harvard Medical School.

The Soviet participants were Chazov, Michael Kuzin, and Leonid Ilyin; while the Americans were Lown, James Muller, and John Pastore.

Discussed was Gorbachev's unilateral moratorium on nuclear weapons testing, the arrest and detention of Nobel Laureate physicist Andrei Sakharov in the city of Gorky, the north–south divide, and other important subjects.

Two organizations founded by Lown, SatelLife (1988) and ProCor (1997) were designed to aid physicians in developing countries by connecting them to relevant information on cardiovascular disease and its prevention.

[25] ProCor’s global outreach included The Ashanti-ProCor Project, launched in 2006, which was designed to assess cardiovascular disease knowledge and practice among health workers in the Ashanti Region of Ghana, identify those who can play a key role in prevention, and explore their information needs as a way to better address the needs of physicians in the developing world.

[31] The Lown Institute addresses the growing crisis in healthcare in the US, marked by overtreatment, undertreatment, and mistreatment through research, clinical programs, and convenings.

The Institute holds an annual conference where the newest research on overuse and underuse is presented, and where like-minded clinicians and patient advocates can share ideas.

Among participants in the leadership of The Lown Institute are Nassib Chamoun, Vikas Saini, Shannon Brownlee, Thomas Graboys, Professor Joseph Brain, Patricia Gabow, Elizabeth Gilbertson, James Joslin, Aretha Davis, David Bor, Michael Fine, and Breck Eagle.

The Right Care Alliance brings together clinicians, patients, and community members in a grassroots movement advocating for a universally accessible, affordable, safe, and effective healthcare system.

The RCA holds an annual week of action, during which members organize activities to demonstrate compassionate, patient-centered care, such as engaging the broader community in listening and storytelling.

"[37] In 2012, a visiting Professorship was established whose function is to coordinate the courses afforded to the Lown Scholars as well as help promote cardiovascular preventative programs in low- and middle-income countries.