LAS VEGAS — Authorities in Las Vegas said Monday that the death of a 20-year-old UNLV football player who was found unresponsive in his studio apartment in February was caused by a heart ailment.

An autopsy found that Ryan Keeler had a disease called hypertrophic cardiomyopathy that causes thickening of the heart muscle, and died Feb. 20 of a fatal irregular heartbeat, the Clark County coroner’s office said in a statement. His death was ruled natural.

Las Vegas police initially investigated Keeler’s unexpected death, pending the medical examiner’s report. Officer Robert Wicks said Monday the inquiry was closed.

UNLV head coach Barry Odom had announced Keeler’s death, calling the 6-foot-6, 275-pound defensive lineman a standout student and athlete. He was from Chicago and arrived at UNLV by transfer from Rutgers University in New Jersey.

Keeler played in seven games as a redshirt freshman for the Rebels and made the academic All-Mountain West team with a 3.8 grade-point average, Odom said.

The university released a statement Monday calling Keeler’s death “tragic and untimely” and expressing sympathy with his loved ones, teammates and friends.