TUCSON, ARIZ. ? University of Arizona center Shawntinice Polk died Monday of a blood clot in her lungs that resulted in “essentially a sudden cardiac death,” the county’s chief medical examiner said.

The 22-year-old Polk, who had knee surgery after last season, had “small, deep-vein clots” in her legs, the medical examiner said. In anyone, these clots can form a large clot that can stop blood flow to the heart.

“Multiple clots end up breaking off the inside of the vein and stack up against one another,” said Dr. Eric Peters, Pima County chief medical examiner.

After the clot or clots travel to the lungs, “essentially it causes a sudden cardiac death,” he added.

Polk collapsed Monday morning after arriving at McKale Center, the school said. She complained of feeling ill, but had not begun to work out or practice, athletic director Jim Livengood said.

UA declined to comment about Polk’s cause of death or whether the player used a UA doctor for her surgery and rehabilitation. A memorial service for Polk will be held at 6:30 p.m. Wednesday at McKale Center.

Polk, a 6-foot-5 senior center, had been in training as part of her recovery from the effects of a December surgery on her left knee.

Both knees had been operated on the previous year to remove cartilage damage before her junior season. She had been complaining of asthma of late and had been suffering from a headcold.

“This is a terribly sad, heartbreaking day in Arizona women’s basketball,” Wildcats coach Joan Bonvicini said. “I can’t put into words the pain and sadness that we’re all feeling right now.”

Polk was the driving force behind a team that went 20-12 and earned an NCAA Tournament berth last season. She was an honorable mention AP all-American selection as a freshman and sophomore.