Tanya Ginther, 26, had given birth to her second child just two months earlier, so she thought it was only natural to feel tired, and out of breath.
But packing the car one day in the garage attached to her Bismarck, N.D., home, Tanya collapsed. Her heart had stopped without warning – a cardiac arrest.
In a police recording of his 911 call, her husband, Mike Ginther, can be heard pleading with his wife to hang on.
"Come on, Tanya, g-----n it! Come on," Ginther can be heard saying. "There you go! There you go honey. Breathe, girl, breathe!"
For 16 minutes, waiting for the ambulance to arrive, Mike Ginther frantically performed CPR on his wife.
Doctors later determined Tanya was suffering from a mysterious condition called peripartum cardiomyopathy.
The condition, which according to the National Institutes of Health strikes as many as 3,000 new mothers in the United States every year, is characterized by symptoms that include fatigue and shortness of breath -- symptoms that resemble those common to new mothers and are therefore often missed.
Experts say they don't know why peripartum cardiomyopathy develops.
"The heart muscle weakens in the last months of pregnancy," Sharonne Hayes, a doctor at the Mayo Clinic, told ABC News. "We don't know what causes it. It could be inflammation, or a virus, or the changes in hormones."
At a Bismarck, N.D., hospital, Tanya Ginther's heart stopped, again and again. Doctors, shocking her back to life each time, predicted she wouldn't survive for more than a day or two.
Her only hope, doctors said, was to get to a major medical center hundreds of miles away, where she could be outfitted with a heart pump.
In a last attempt to save her life, the Mayo Clinic dispatched one of its "air ambulances," a Learjet equipped with the latest emergency medical equipment, to lift Tanya to its hospital in Rochester, Minn.
But at an altitude of 30,000 feet, Tanya's heart failed yet again.
"She arrested on us and we had to shock her heart back into rhythm," said Tim Alden, the Mayo Clinic air nurse on duty that day. "For about 45 minutes there in the flight we were holding our breath."
By the time Tanya reached the Mayo Clinic, her organs were shutting down from lack of blood. Doctors now said she was too sick to have the heart pump surgery.
"They said, 'We're sorry, but she's going,'" Mike Ginther told ABC News.
Surprisingly, Tanya's condition improved ever so slightly, enough at least to get that artificial pump. And with each passing day, and the help of that pump, her heart gained strength.
Within a month, Tanya was back home with her family, and the pump was soon disconnected.
Doctors now say Tanya's story should be a warning to any new mother.
"If you're really short of breath, or feeling light-headed, or you continue to swell," Hayes said. "You need to see a doctor."
Tanya Ginther agreed. She says pregnant women and new mothers should be watchful for the signs of peripartum cardiomyopathy.
"Don't feel like you're overreacting," she told ABC News. "When it comes to your heart and your life, you can't overreact."
ABC News' Christine Brouwer contributed to this report.