Morton Mower, an entrepreneurial cardiologist who helped invent an implant that has saved many lives by returning potentially fatal irregular heart rhythms to normal with an electrical shock, died in Denver on April 25. He died at the age of 89.

Mark said the cause was cancer.

In 1969 Dr. Mower and Dr. Mirowski began work on a small device that could be implanted under the skin of the abdomen to correct a heart problem.

Dr. Mirowski and Dr. Mower both believed it could be done.

In an interview with the medical journal The Lancet in 2015, Dr. Mower said that they were the crazy guys who wanted to put a time bomb in people's chests.

The doctors formed a partnership with Medrad in 1972 after developing a prototype. Critics criticized the development of an implant.

Dr. Bernard Lown, who invented the first effective external defibrillator, and Dr. Paul Axelrod, who is a cardiovascular surgeon, wrote in Circulation that patients with ventricular fibrillation were better served by surgery or an anti-arrhythmia program.

The implanted defibrillator system is an imperfect solution in search of a plausible and practical application.

The work continued. The battery-operated device, which was the size of a deck of cards, was first implanted in humans in 1980. Five years later, it was approved by the FDA.

The F.D.A. said that if people could have their arrhythmia corrected quickly, they would be less likely to die in hospital emergency rooms.

According to the American Heart Association's president, 300,000 small devices are implanted annually.

Dr. Lloyd-Jones said that letting people walk around with a defibrillar was revolutionary in saving the lives of people at risk of fatal heart attacks.

He said that the device's electric shock is delivered directly to the heart, which makes it an advantage. The shocks must travel through skin and tissue before they reach the heart.

In 2002, Dr. Mower and Dr. Mirowski were joined in the Inventors Hall of Fame by M. Stephen Heilman, a project engineer at Medrad.

ImageDr. Mower with his wife, Toby, a registered nurse.
Dr. Mower with his wife, Toby, a registered nurse.Credit...Jewish National Fund-USA, via Associated Press
Dr. Mower with his wife, Toby, a registered nurse.

Morton Maimon Mower was born in Baltimore on January 31, 1933, and grew up in Frederick, about 50 miles away. His parents were both homemakers and Robert was a cobbler.

During the summers, Morton worked for his Uncle Sam, who owned bathhouses and a toy store in Atlantic City. When his uncle got sick, Morton was impressed with how the family treated the doctor.

In an interview with the alumni magazine of the University of Maryland School of Medicine, Dr. Mower said that they made him sit down and have a cup of tea. I would like to do that.

After graduating from medical school and earning a bachelor's degree, Dr. Mower worked at the University of Maryland Medical Center.

He was chief of medicine at the Army Medical Corps in Germany from 1963 to 1965, after he became chief resident at Sinai Hospital.

He was an investigator for six years in Sinai's coronary drug project. He became the chief of cardiology at the hospital. A building on the campus was named after him.

Dr. Mower used his money to build a large art collection that included works by Rembrandt, Picasso and Impressionist masters.

He worked for two companies after leaving Sinai: Guidant as a consultant and a subsidiary of Eli Lilly as a vice president. He taught medicine at the University of Colorado in Aurora.

Dr. Mower created a company called Rocky Mountain Biphasic to find commercial uses for his many patents in areas such as cardiology, wound healing, diabetes and Covid-19.

He is survived by his wife, Toby (Kurland) Mower, a registered nurse, a daughter, Robin Mower, three grandsons, a brother, Bernard, and a sister, Susan Burke. He lived in Denver.

The work done by Dr. Mower in resetting the heart didn't end with the device.

He told The Lancet that it did nothing to support left ventricular function. People were dying of heart failure.

He and Dr. Mirowski came up with the idea of cardiac resynchronization therapy, or C.R.T., which uses an implanted device to send electrical impulses to the right and left ventricles of the heart in order to force them to contract in a more.

It was almost unbelievable how big of an advance C.R.T. was.