WATERLOO - Mary Jo Scully Klatt believes she has a guardian angel - an angel who kept her alive as she ignored symptoms that should have led to a fatal heart attack.

Klatt underwent an emergency double bypass last summer after a stress test showed a major blockage in an artery. The vessel was 90 percent blocked, and the blockage was in a location difficult to access.

"I had what was called a widowmaker, which means if I would have had a heart attack I would not have survived," says Klatt.

Klatt and her family and friends were stunned at the discovery. She was just 54 and had been an aerobics instructor for 20 years.

"I exercised almost every day, was not overweight, never smoked, didn't have extremely high cholesterol and didn't have diabetes," says Klatt. "My genes had taken over, my arteries were clogged and I was headed for double bypass surgery."

Dr. Kalyana Sundaram, an interventional cardiololgost with Cedar Valley Medical Specialists, says that's a common reaction among heart patients who have none of the risk factors for heart disease.

"People say 'I walk every day, I exercise; eat right. Where did I go wrong?' Probably that's why you are still alive. If you haven't done any of those things, maybe you would have died of a heart attack four years ago. It wasn't a waste."

Sundaram says exercise conditions the heart, and in people with blockages the heart gradually learns to live with insufficient oxygen. Over time, natural bypasses form around the blockage.

Klatt first experienced symptoms long before the surgery. She was participating in a step aerobics class when she felt a pain in the center of her chest that radiated through her shoulders. She thought it was heartburn and took an antacid. The pain subsided.

Over the next 18 months, the bouts of pain would come and go, always when Klatt was in motion. She continued taking antacids to curb the discomfort. Sundaram says people often mistake serious heart symptoms with heartburn. But it's not the antacid that stops the pain, rather the cease of activity.

"There is a burning sensation in the chest. Most of the time it is associated with exertion and it goes away when you take a rest," he says. "But it's not too uncommon to blame the pizza. When it happens periodically, you must have it checked to make sure it's the pizza and not something serious."

When the pain and subsequent shortness of breath forced Klatt to sit down in the middle of an aerobics class she was teaching, she returned to the doctor seeking a stronger antacid. The doctor scheduled her for a stress test instead.

"I was excited to get all this over and get to the bottom of this pain," Klatt says of the morning she went for the test. She was sure she would pass with flying colors. "I drove off with a car full of goods for Goodwill, my workout clothes for after the stress test and notes for a meeting at noon."

For the stress test, Klatt was hooked up to heart monitors and hopped on a treadmill. The doctor started her out at a quick pace. Almost immediately, Klatt became winded and had chest pain.

"They stopped the treadmill, sat me down and gave me some aspirin," she recalls. "I was in a hospital room within an hour."

Two days later, she had double bypass surgery at Allen Hospital.

Sundaram says Klatt was fortunate. Most patients who ignore symptoms don't live to tell about it. People who are at risk for heart disease - family history, high cholesterol, high blood pressure, a sedentary lifestyle - should be especially concerned if they experience symptoms. Symptoms can include shortness of breath with activity; chest pain or a feeling of tightness or pressure in the chest; or a burning sensation in the chest.

"It's important to pay attention. If you catch early on, with a simple test a doctor may be able to prevent a heart attack," Sundaram says.

June 18 marks the anniversary of Klatt's surgery. It was six weeks after the bypass before she entered rehabilitation.

"I was looking so forward to going back to exercising, but the first day of rehab I cried," she says. "I could barely walk on the treadmill for five minutes. I went from being a physically fit specimen to barely being able to walk 10 feet."

Klatt was released from rehab when she started riding her bicycle to rehab sessions.

"I guess they considered me healed," she says, laughing.

Contact Meta Hemenway-Forbes at (319) 291-1483 or meta.hemenway-forbes@wcfcourier.com.