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AP Photo/GoldenBearSports.com, Nathan Phillips

Ted Agu

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AP Photo/GoldenBearSports.com, Michael Pimentel

This Oct. 12, 2013 photo released by GoldenBearSports.com shows California's Ted Agu, right, tackling UCLA's Damien Thigpen, in Pasadena, Calif. Agu died Friday morning, Feb. 7, 2014. He was 21. The school announced Agu's death and said its thoughts and prayers were with Agu's family, friends and teammates.

A Cal football player and Frontier High graduate, who died in February after collapsing on a training run, died from an inherited heart condition, media outlets from the San Francisco area reported Wednesday.

Ted Agu, 21, died of hypertrophic cardiomyopathy, a rare, abnormal thickening of the heart muscle which can make it harder for blood to leave the heart, San Francisco public television station KQED reported in a blog, adding that the condition leads to cardiac arrest in less than 3 percent of people with the condition.

Both KQED and the San Francisco Chronicle listed the Alameda County Coroner's Office as the source of its stories detailing the cause of Agu's death.

Both media outlets reported that Agu's condition is a well-known cause of death for young athletes. The Chronicle listed notable basketball players Hank Gathers and Reggie Lewis among those who died from the condition.

"In roughly 50 percent of cases, they could have no symptoms at all, and the very first symptom could be a cardiac arrest," Dr. Kishor Avasarala, who specializes in sudden cardiac death risk at UC San Francisco's Benioff Children's Hospital Oakland, told KQED.

Agu, a junior defensive end, collapsed during a supervised training run about 6 a.m. on Feb. 7. He was reportedly alert when put on a cart, but collapsed when he got back to Cal's Memorial Stadium, according to The Chronicle.

CPR was started immediately and a defibrillator was used, authorities told The Chronicle, but Agu later died at Alta Bates Medical Center in Berkeley.

According to The Chronicle, it is not known whether Agu knew of the ailment, which is "generally not compatible with competitive athletics," according to the Hypertrophic Cardiomyopathy Association.

Avasarala also told KQED that even though symptoms are rare, red flags can include unexplained fainting episodes, -- especially incidents related to exercise -- and a family history of heart problems.

Cal team physician Dr. Casey Batten, in a Feb. 7 ESPN story, said Agu never had any previous problems with workouts or practices during his time at Cal.

"I've been with Ted since he got here and he's never had any problems during any workout or practice," Batten said in the ESPN story.