Helen Seth-Smith, 82, of Great Falls went to the McLean Hardware store yesterday because her large green flashlight wasn't working. While she was standing at the counter, her heart stopped working and she collapsed on the brown carpet between the checkout register and a display of toasters and pots.

Seth-Smith was alive last night, reported in stable condition at Northern Virginia Doctors Hospital, and Fairfax County fire and rescue officials credited an 18-year-old clerk at the store with saving her life.

The clerk, Danny Treu of Falls Church, had learned CPR (cardiopulmonary resuscitation) in his 11th-grade health class at McLean High School.

Mike Cannon, who was running the cash register, shouted for someone to call the fire department when Seth-Smith collapsed and called for Treu, who was in the back.

Treu said he found the woman turning blue, without a pulse and not breathing. Almost without thinking, he recalled, he started to apply the technique he had previously used only on the plastic dummy his school used to teach CPR.

"It's much different when you're doing it on a real person," he said.

But it worked. Treu said he administered one set of 15 chest compressions and one burst of mouth-to-mouth resuscitation, "and she came right back -- she started breathing again."

By then, paramedics had arrived from the McLean fire station, which is around the corner, and they took the woman to the hospital.

Seth-Smith was a teacher and assistant to the headmistress at the Potomac School in McLean for 35 years until the mid 1960s, and was active for many years in the Girl Guides, teaching, among other things, first aid.

Treu, who has been a volunteer at the fire station and hopes to join the fire department next year, suspected that everyone was kicking up too much fuss about what he did.

"I think you can make too big a thing about things like this sometimes," he said. "I'm sure somebody would do the same thing for me."