Peter Cai, a Harvard University junior from McCandless known for his brilliance, kindness and common sense, died Saturday of a heart attack after running in a footrace.

Mr. Cai, 20, a pre-med major in molecular and cellular biology who graduated from North Allegheny High School in 2006, collapsed after completing the race along the Charles River. Despite immediate attention from two nearby anesthesiologists, he was pronounced dead at Mount Auburn Hospital. He was a championship swimmer in high school and friends knew of no history of heart trouble.

He was considered one of North Allegheny's most promising graduates.

"We always figured he would be the guy who cured cancer. He was that good," said Kirk "Corky" Semler, head swimming coach at North Allegheny.

He was the only child of Ming Ding and Quan Cai.

"They put their heart and soul into trying to raise that kid the right way and do everything that good parents should do," Mr. Semler said.

His name began appearing in the Pittsburgh Post-Gazette at age 9 for winning math competitions.

"He was one of our stellar students," said math teacher Sharon Volpe, who taught him AP calculus in 10th grade.

He spent two high school summers at the University of Pittsburgh Graduate School of Public Health's Department of Environmental and Occupational Health researching "the role and catalytic redox mechanisms of cytochrome c in the oxidation of phosphatidylserine and cardiolipin during cell apoptosis." The team study of how the immune system responds to infections was published in 2007 by the prestigious Journal of Biological Chemistry.

"He was extremely bright, very pleasant, very talented. Although you usually cannot expect it of a high school student, he was trusted to conduct experiments," said Valerian Kagan, the professor who supervised him.

Some faculty have difficulty getting into the journal he was published in, but he earned it, Dr. Kagan said. "His name was rightfully put there and that's a big achievement for a student."

He was an accomplished violinist with the Pittsburgh Youth Symphony Orchestra. He found time to volunteer at the Carnegie Science Center and Mercy Hospital and to lead sing-alongs at the Kane Regional Center Nursing Home.

He was on the varsity swim team, and was a WPIAL finalist in the 100-yard breaststroke.

"He wasn't an especially talented swimmer, but he was a hard worker who listened. He would stay after practice just to work on stuff. That's unusual in our sport, where practices are so long and grueling," Mr. Semler said.

Some of his teammates weren't as bright, but "I never heard a condescending word come out of his mouth. He was always supportive and understanding," Mr. Semler said.

Mr. Cai earned perfect scores in the math, verbal and foreign language SATs. He was a National Merit finalist and received the Pennsylvania Council of Teachers of Mathematics Outstanding Student Achievement Award, the U.S. President's Award for Educational Excellence and first prize in the Pennsylvania Junior Academy of Science.

He continued to excel at Harvard. While keeping up his school work, he played violin with the Mozart Society, tutored students in Boston's Chinatown, and was a certified CPR instructor and co-director of Harvard Emergency Medical Services. That group had traditionally focused on teaching CPR to Harvard students, but Mr. Cai pushed to teach in disadvantaged Boston neighborhoods, said Anupriya Singhal, his co-director.

"He wanted to build a sense of community in the organization and he wanted the volunteers to understand the importance of what they were doing," Ms. Singhal told The Harvard Crimson.

Mr. Cai's parents attended a memorial service for him yesterday in the Harvard chapel. Local arrangements were incomplete.