DENVER (AP) -An autopsy on Denver Broncos running back Damien Nash found no drugs or unnatural substances of any kind in his system. An exact cause of death could not be determined, the St. Louis County medical examiner's office said Tuesday night.

Nash, 24, collapsed and died Feb. 24 after a charity basketball game he hosted in St. Louis, his hometown. Nash arranged the game at his high school to benefit The Darris Nash Find a Heart Foundation, which was named after his 25-year-old brother, who had a heart transplant last year.

A representative from the medical examiner's office said the cause of death was listed as ``undetermined.''

``It was a natural death of cardiac origin, but we were unable to determine the exact origin,'' said the representative after consulting Dr. Mary Case, chief medical examiner for St. Louis County.

After playing for the University of Missouri, Nash was a fifth-round draft choice by Tennessee in 2005.

He played in three games for the Titans before the Broncos signed him as a free agent last season. He played in three games for Denver, 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.Copyright © 2005 The Associated Press. All rights reserved. The information contained in the AP News report may not be published, broadcast, rewritten or redistributed without the prior written authority of The Associated Press.