The father of a 19-year-old woman who died Sunday while running in the Marine Corps Marathon said yesterday an Arlington police officer told him his daughter's heart attack stemmed from a congenital condition.

Lisa B. Christensen, a sophomore at Boston University, collapsed on the 14th Street Bridge a little more than two miles short of the finish of the 26.2-mile race. She died later at Arlington Hospital.

"He said that he'd gotten the report and it indicated that a genetic heart problem caused Lisa's death and that it does not always show up on medical tests," said Hans Christensen of Cheshire, Conn., of the call from the Arlington police, in whose jurisdiction the incident occurred. "He explained that there are two arteries that {supply blood} to the heart and that they {usually} go in at two different spots and in her case they both came in at one spot. Evidently, there was too much pressure."

An Arlington police source confirmed last night the heart failure was the result of a congenital heart problem.

Christensen, who was running her first marathon, was a midshipman in the Naval Reserve Officers Training Corps running with ROTC classmates. She reportedly was unconscious with a weak pulse after she fell at about 1:15 p.m. She was treated at the scene and taken by the Wheaton Rescue Squad to the hospital, where she died at 2:45 p.m. A spokeswoman for the hospital said Christensen went into cardiac arrest in the ambulance, which arrived at the hospital at 1:42 p.m.

Barbara Lowery, 38, an exercise technician at Southeastern General Hospital in Maxton, N.C., was running behind Christensen when she saw her slump over. "She looked like rubber," said Lowery, also running her first marathon. "She must've been 14 feet ahead of me and I didn't notice anything different. But she just went down. It was weird-looking, like something that loses all control. She went over on her side, limp, and I knew something was wrong."

Lowery said two police officers, who were positioned nearby, reacted immediately, covering the fallen runner with blankets to prevent her from going into shock and speaking into their walkie-talkies. Another runner also helped.

"They handled it real well," Lowery said. "One guy turned her over. . . . She was having convulsions. And the ambulance was there in a flip. . . .

"There was just something about her, I don't know what it was. I had my eye on her. I don't know, maybe it was instinct. She was doing good. . . . Then, all of a sudden, poof."

Bill Supp, the amateur radio operator assigned to the Wheaton Rescue Squad ambulance, entered a tense situation seconds after he radioed the emergency to medical headquarters. "Immediately after we started moving, the medic asked me to help him," Supp said. "He said, 'Put down the radio, I've got something more important for you to do.' "Staff writer Stephanie Griffith contributed to this report.