PHILADELPHIA (CBS)—On this National Walking Day, a fitness tracker that counts steps is credited with saving a woman’s life.

Patricia Lauder bought a fitness tracker to count her steps and help her lose weight.

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“That was the main reason I bought the Fitbit initially,” she says.

But now the 73-year-old credits the device with saving her life.

A few months ago, she wasn’t feeling well. She thought her sinus infection may have turned into pneumonia.

“I went to the doctors to have that checked out and that turned out to be negative,” said Lauder.

Then she noticed her resting heart rate on her Fitbit was climbing higher and higher every day.  She had shortness of breath and her heart rate spiked to 140 beats per minute. She called for an ambulance.

“When it finally got to the point where walking across the room was a major issue, I picked up the phone and knew I needed help,” she said.

A CT scan uncovered a potentially deadly problem: two pulmonary embolisms or blood clots.

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“That showed a large clot in the lung artery in both sides,” said Dr. Juyong Lee, assistant professor in the Department of Medicine at UConn Health.

Her heart was also enlarged.

Because the blood clots in the lung put strain on the heart, causing blood pressure and oxygen levels to drop dangerously doctors gave Pat clot busting drugs right away. By the next day,  her clots were gone.

Pat says without her Fitbit, she may not be here to tell her story.

“It certainly helped me under the most recent circumstances,” said Lauder.

Pat’s lung and heart function has returned to normal.

She’s now counting her blessings and back to counting her steps, too.

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Doctors say people shouldn’t rely on fitness trackers to routinely monitor health conditions