The Denver Broncos' running back died Saturday and the cause remained unclear Sunday, but his grieving mother knows what she must do.

After one son's death and a heart ailment that caused another son to require a transplant last year, Kim Nash is taking her daughter to a cardiologist next week.

''My son,'' she said amid sobs, ''is giving me the strength right now to talk.''

Damien Nash collapsed in his suburban St. Louis home after returning by limousine with his wife, Judy Nash, and their daughter from a game at his high school to benefit The Darris Nash Find a Heart Foundation. The organization raises money for heart transplant research.

The 24-year-old player was taken by ambulance to Christian Hospital Northeast, where he was pronounced dead. The hospital's nursing supervisor, Maria St. George, told the AP the hospital dispatched an ambulance as soon as it received the call.

The St. Louis County medical examiner's office said results of Sunday's autopsy may not be known for days, even weeks.

''I didn't see anything to point to a cause of death,'' Dr. Kamal Sabharwal, the medical examiner, said late Sunday.

He said he was waiting on lab results to check for drugs or alcohol, and a look at tissue sections. He's also asked a forensic pathologist who specializes in hearts to look at Nash's heart.

Dr. Gregory Ewald, a cardiologist, treated 25-year-old Darris Nash and said he had a weakened heart muscle condition known as dilated cardiomyopathy. The ailment can be caused by a viral infection, inflammation or other causes. Darris Nash became so ill he needed a mechanical device to support his circulation until he could get a transplant.

Ewald said some cardiomyopathy conditions run in families. He said he never met Damien Nash, but ''the fact that Damien was doing high-level athletics may indicate that was not the problem.''

The death comes less than two months after the still unsolved slaying of Broncos teammate Darrent Williams. Damien Nash's agent, David Canter, said the Broncos were trying to contact teammates, who have scattered for the offseason. Funeral arrangements were not yet set.

Canter said that Nash had four physicals since 2004 and was in good health. He said the Broncos planned their own investigation.

Canter said Nash had been ecstatic last week organizing the charity game. His client's high school coach, Darren Sunkett, said Nash had invited some NFL players from the St. Louis area and some former University of Missouri players. He was talking to a cousin when he collapsed.

The agent said dozens of family members had gathered at Nash's house for a celebration or were en route when he died. Judy Nash, he said, recalled that her husband hadn't been drinking or partying, adding that ''all he cares about is his daughter and this event.''

Canter said Nash's friends and family take comfort in knowing that in his last moments he was surrounded by ''every single person that loves him, that he loved and that loved him back.''

Sunkett, whom Nash followed from Riverview Gardens High School in suburban St. Louis to East St. Louis (Ill.) High School, added: ''He was a very humble, bright kid, always funny and enthusiastic. ... You couldn't dislike him.''

A fifth-round draft choice by Tennessee in 2005, Nash played in three games for the Titans. The Broncos signed him as a free agent last season. He played in three games, rushing for 66 yards on 18 carries. In his two-year career, he had 24 carries for 98 yards and seven receptions for 55 yards.

Missouri coach Gary Pinkel said the Tigers were in shock over Nash's death, which happened less than two years after Missouri football player Aaron O'Neal died during summer workouts in 2005.

News of Nash's death spread quickly to Coffeyville Community College in Kansas, the school he attended before heading to Missouri.

''They don't make them no better than Damien,'' Coffeyville running backs coach Dickie Rolls said. ''He was such a competitor.''