A heart attack killed 39-year-old endurance athlete Steve Larsen, who collapsed last month while running, the Deschutes County medical examiner said Wednesday evening.

Steve Cross, the medical examiner, said tests showed Larsen had atherosclerosis, or coronary heart disease, that resulted in a heart attack.

“Unfortunately, sometimes the first indication of heart disease is sudden death,” Cross said.

Larsen, a former champion mountain bike rider, runner and elite triathlete collapsed May 19 while working out on the Cascade Middle School track. An autopsy left questions about the cause of his cardiac condition, and his heart was sent to a laboratory in the Midwest for analysis.

Cross pointed out Wednesday that even the most fit person can suffer a heart attack.

“Nearly 1 million people will die this year, and about half of them will die of heart disease,” he said.

Michael Larsen, 41, of Bend, Steve’s older brother, said the news is hard to hear.

“I’m glad to get the information, although none of it’s good, and it doesn’t make me feel better,” he said. “But to have the information is important. To know that your first symptom could be sudden death, it’s important to know that any breath could be your last breath.”

Michael Larsen, also an athlete, said since his brother died, he has already made some changes to his life. He’s asked his parents about their health history, and plans to make a doctor’s appointment for himself soon.

“My dad does have an enlarged heart and cardiomyopathy, which are both hereditary” Larsen said. “It’s a little scary because I haven’t had heart tests done, and I didn’t know (my father’s) heart issues were those issues. … My doctor has requested to see me ASAP.”

Michael Larsen said it also makes him think about his two sons, as well the five children Steve left behind.

“It’s definitely made me more cautionary,” said Michael Larsen, who mentioned he recently took out a health insurance policy.

“You definitely re-prioritize some of the things in your life,” he said. “But I think I live a healthy lifestyle of fitness and family, which is kind of what you do around here. Which was a scaled down version of what Steve does.”

Along with his children, Larsen left behind his wife, Carrie. The Web site www.worldtri.com is accepting donations to the Steve Larsen Memorial Fund.