San Francisco 49ers offensive lineman Thomas Herrion had heart disease and likely died from an arrhythmia after playing in an NFL preseason game last month, the doctor in the Denver coroner's office who performed his autopsy said yesterday.

Amy Martin said that Herrion's weight, his family history of heart disease and the exertion of playing in the Aug. 20 game in Denver probably were among the factors that contributed to his death.

The Denver Office of the Medical Examiner announced that it had completed its autopsy on Herrion, who collapsed in the 49ers' locker room after the game against the Broncos and was pronounced dead later that night at St. Anthony Central Hospital, and found the cause of his death to be ischemic heart disease. The office said in a written statement that Herrion, who was 23, had "significant blockage" of his right coronary artery that "had caused death of heart muscle," and his heart was "slightly enlarged." The coroner's office said that a "comprehensive" drug screen of Herrion's blood and urine found only atropine, a drug used to try to revive him.

Martin said in a telephone interview she could not determine for certain whether Herrion's ischemic heart disease had caused him to die by a massive heart attack or by an arrhythmia, an irregular heartbeat or abnormal heart rhythm, that was so abnormal it left his heart unable to function, but she thinks it probably was an arrhythmia.

"That's probably what happened here," Martin said. "Although it's possible he had a massive heart attack, more than likely he had an arrhythmia."

According to the American Heart Association, cardiac ischemia is a condition in which narrowed arteries restrict blood flow (and thus oxygen) to the heart. It also is called coronary heart disease and coronary artery disease, and an estimated three to four million Americans may have ischemic episodes without knowing it and are at risk of suffering heart attacks without prior warning.

Martin said that Herrion was "pretty young for coronary heart disease" but "heredity probably played a role" in his condition. His father had diabetes and died from a stroke, and his mother suffers from high blood pressure. Herrion was listed at 315 pounds in the 49ers' media guide, and Martin said: "Any time you're overweight, it causes your heart to work harder. Anything that causes your heart to work harder can set you up for something like this. If he'd weighed less, his risk would have been lessened but not taken away."

She said that Herrion playing in the game "probably had a role" in his death. "You certainly see a lot of people with ischemic heart disease die after exertion. But sometimes they die in their sleep or die watching TV."

She indicated she was not surprised that Herrion's condition had gone undetected. "Most of what he had is not something that's going to be detected in a routine physical," Martin said. "Even if he had an EKG [electrocardiogram] done, it's not going to show any abnormalities."

NFL Players Association chief Gene Upshaw said the league "can't legislate weight," and will continue to have teams conduct annual medical exams as comprehensive as science allows. Tom Mayer, a medical adviser to the union, said the only test that might have detected Herrion's condition is a cardiac catheterization.

"You'd have a hard time finding anyone who would do that to a seemingly healthy 25-year-old athlete unless there were symptoms beforehand," Mayer said.