Diane Marofske can remember the moment she started to feel the pain creep along her left arm.
"That's different, that's not right," she remembers thinking. Then the pain intensified, and pretty soon "I had chest pain, and then it started to get harder to breathe," said the 50-year-old Rochester, Minn., woman.
Today, six months after suffering a heart attack, Marofske said, "I feel better than I did pre-heart attack, and people tell me that I look better too."
In all likelihood, Marofske's fast recovery can be attributed to the cardiac rehab program she began two weeks after her surgery. Applying training methods that have long helped athletes improve performance, the Mayo Clinic has urged its cardiac patients to apply the principles of high-impact interval training to speed their recovery.
The patients -- recovering from heart attacks, bypass surgery, heart failure and coronary artery disease -- undertake workouts that consist of short bursts of intense exercise, pushing themselves to heart rates of up to 95 percent, followed by periods of more exercise at a more moderate pace.
Markofske said she walks at varying speeds on a treadmill.
"They're going to a greater increase in cardiovascular fitness, they're going to see a faster increase in cardiovascular fitness," said Ray Squires, program director of the Cardiovascular Health and Rehabilitation Center at Mayo Clinic.
Conventional wisdom for cardiac rehabilitation has long called for patients to start exercising slowly, at fairly low-intensity, and gradually increasing it in duration, up to 45 minutes, but at a relatively steady pace of about 60 percent of the patient's exercise capacity.
Yet for the past four years, cardiac patients at the Mayo Clinic have been interval training, which allows the heart to pump more blood and transport more oxygen to the skeletal muscles, producing more energy during exercise.
While athletes have been interval training for many years, and its use for cardiac patients has been studied intermittently since the 1990s, the practice is still controversial. Mayo is one of the only medical facilities in the U.S. to use intense interval training in the early stages of cardiac rehabilitiation.
"We have yet to show that this kind of rehab will have long term impact in terms of making people live longer or stay out of the hospital," said Dr. Marrick Kukin, a cardiologist at St. Luke's-Roosevelt Hospitals in New York.
That may be, but Squires is confident that interval training has helped his patients. "It probably improves blood pressure, and improves the ability of the patient to process blood sugar," he said. "And it probably improves mood."
Squires believes that up to 90 percent of the heart patients the Mayo Clinic sees could benefit from the training, though only a much smaller portion choose to participate.
Interval training is not recommended for those with angina or chest pain during exercise, nor for patients with high or low blood pressure or those with muscle aches and pains.
"Age is not a contraindication for this program," Squires said. "We've had patients go through the program who are in their 90s."
The physical effects of a healthier heart extend to emotional well-being, Squires said, and that's a crucial component of recovery.
"Telling patients that they don't have to "baby" themselves," he said, "they can actually push themselves harder -- I think it improves their self-reliance, their confidence."
After her heart attack, Marofske was nervous about working out. She could barely walk up a flight of stairs. She had fallen out of the habit of exercising years earlier, and before the heart attack, the only thing she did that came close to exercise was walking her dog.
Now she leaves her cardiac rehab sessions feeling more confident. She has joined a gym. And for fun, she and her husband ride a tandem bicycle.
"I wasn't expecting to be able to do the level of workout that I'm doing now," she said. "I'm really pushing myself.
"There is no cheating," she said, laughing, since the heart monitors she is hooked up to at rehab would give that away. "I work up a pretty good sweat. I feel really good."