The 19-year-old Boston University female student who died Sunday while running in the Marine Corps Marathon was the victim of a heart attack, according to the doctor who performed an autopsy yesterday.

Lisa B. Christensen, who was stricken a little more than two miles short of the finish of the 26.2-mile race, died at Arlington Hospital at 2:45 p.m. Sunday.

James C. Beyer, Northern Virginia medical examiner, said the cause of death was a heart attack, not a head injury as a race official had speculated after receiving early reports Sunday.

Hans Christensen of Cheshire, Conn., said there was no medical problem or history of family health complications that would indicate his daughter would die while running a distance race. She had been an athlete since high school, competing on the track and swim teams. "She took care of herself," he said.

"She liked running and she liked the sense, the feeling she had when running. I think she also liked to compete as an individual rather than {in} the team sports," he said. "She liked pushing herself for herself."

His daughter never had run a marathon before, and her father said he did not know how much she ran in preparation for the Marine Corps race. He said she had spoken of running five to eight miles a day, but that he could not be sure.

He was sure of her love for the sport. "She just wanted to {run the marathon} so badly, what can you do?" he said. "It was really important to her. She sent out letters to friends and relatives about the race.

"Her little brother just got a letter from her -- his birthday was Oct. 31 -- and in it she said, 'When I come home from the marathon I'm looking forward to the two of us going out running.' He's a keen runner himself."

Lisa and younger brother Arne, a runner on his eighth-grade track team, also shared a love for animals. Lisa worked several summers in a veterinary clinic near the family's home. "Living creatures took to the both of them, they had a real thing with animals," said their father. "It was satisfying to see that."

Lisa Christensen, a sophomore and a midshipman in the Naval Reserve Officers Training Corps, was running the marathon with 14 fellow ROTC class members. It was through her older brother, Kaj, an ROTC student at the University of Pennsylvania, that Lisa became interested in getting an ROTC scholarship.

"She went down there and visited him several times and looked at the program and saw the other girls and was impressed with what they were doing," said Hans Christensen. "She was interested in the Marine Corps. She saw it as a challenge. When you think of the traditional Marines, you think leatherneck, boy, and she felt that as a woman she could contribute a great deal. She realized she had many opportunities as a Marine, but it was a little too early for her to determine what she wanted to do."

The Marine Corps Marathon was also important to her and her friends because they would be commissioned Marine officers on graduation. They also were raising money for the Shriners Children's Program, and she had contacted friends and family to pledge money per mile.

Lisa Christensen was born in Vienna and lived for many years overseas. Her father, a former international banker, is an international business consultant. He said he emigrated from Norway because he was looking for the greater opportunities provided in the United States. He said he thought his daughter was making the most of her opportunities.

But now his daughter's death has raised some disquieting questions in his mind.

"I guess it's difficult to say I'm satisfied," he said about medical response at the race. "We still don't know everything. We will be getting the report from the medical examiner.

"I am frightened for my youngest son."

Lisa Christensen is believed to have been stricken at about 1:15 p.m., after 4 hours 15 minutes of running. A race official said she was unconscious with a weak pulse at the race site. She was treated at the scene and en route to Arlington Hospital by the Wheaton Rescue Squad. A spokeswoman for the hospital said Christensen went into cardiac arrest in the ambulance and arrived at the hospital at 1:42 p.m.

Don Darby, ham radio communications coordinator for the race, said that he was informed by ham radio operators stationed on the bridge that runners informed the nearby of Christensen's fall. Darby said the radio operators on the scene estimated that the ambulance arrived within two minutes, though it had to move against the the flow of runners.

Darby, who was at medical headquarters, said he was notified by the ambulance radio operator once the ambulance reached Christensen.

Two radio operators were stationed close to the incident and another rode with the Wheaton Rescue Squad vehicle. About 300 medical personnel staffed eight field stations and the main medical headquarters at the start/finish area. There were 20 ambulances along the course. More than 80 volunteer amateur ham radio operators also were dispersed along the course, manning the aid stations and the water stations.

"I don't know if the radio operator saw her go down, but he probably did," said Darby. "Just about every foot along the course was visible from amateur radio operators. We were as staffed and as prepared as anyone could be. There was very little else we could do better. A runner going down is an obvious problem. He called right away when he saw her down."

A Marine spokesman said yesterday that race officials were waiting to receive the medical examiner's report. The Marines also were awaiting the results of their own investigation. "There are still a lot of questions we're not sure of," said Robert Schultz, the medical coordinator of the race and the medical director at Quantico. Washington Post Staff Writer Patricia Davis contributed to this report.