When Georgia Bowen was born by emergency cesarean on May 18, she took a breath, threw her arms in the air, cried twice, and went into cardiac arrest.

The baby had had a heart attack , most likely while she was still in the womb. Her heart was profoundly damaged; a large portion of the muscle was dead, or nearly so, leading to the cardiac arrest.

Doctors kept her alive with a cumbersome machine that did the work of her heart and lungs. The physicians moved her from Massachusetts General Hospital, where she was born, to Boston Children’s Hospital and decided to try an experimental procedure that had never before been attempted in a human being following a heart attack.

They would take a billion mitochondria — the energy factories found in every cell in the body — from a small plug of Georgia’s healthy muscle and infuse them into the injured muscle of her heart.