LAKE BUENA VISTA, Florida Even though the parents of a 12-year-old boy who died after riding a Walt Disney World roller coaster said he was healthy, a medical examiner determined Friday that the boy in fact had a congenital heart defect.

The autopsy of Michael Russell was done one day after he passed out while riding Disney-MGM's Rock 'n' Roller Coaster. He was pronounced dead at a hospital. The cause of death was natural, ruled Dr. Jan C. Garavaglia, Orange County's chief medical examiner.

"No evidence of injury was found but congenital heart abnormalities were detected, which will be further evaluated. The cause of death will be left pending until results of the additional studies are obtained," the office said in a statement.

Byron Russell noticed his son, Michael, became limp while they rode the Rock 'n' Roller Coaster along with his mother and 7-year-old brother Thursday morning.

When the minute-long ride finished, Byron Russell pulled Michael off the ride and performed CPR, said Barbara Miller, Orange County Sheriff's Office spokeswoman.

Deputies said a ride employee called 911 at 11:20:36 a.m., summoning paramedics from Reedy Creek Fire Rescue, the Orlando Sentinel reported Friday. Click here to read the Sentinel story.

Paramedics stationed at the park arrived about three minutes after the 911 call came in and took over resuscitation efforts from the Army Green Beret father, the Orlando paper reported. Disney has portable heart-defibrillator units stationed throughout its parks but apparently there was not one available to use on Michael until the paramedics arrived, according to an audiotape of the 911 call.

The child's heart was first shocked 7 minutes and 3 seconds after the 911 call.

The boy was pronounced dead after he was taken by ambulance to Celebration Hospital, Disney said in a statement. The cause of death was not immediately determined and medical examiners planned to perform an autopsy Friday.

"According to the family, he was a very healthy child," Miller said. "The father repeated that he was healthy, he had no problems."

Byron Russell is a part of the 5th Special Forces Group (Airborne) based at Fort Campbell, Ky., and served in Iraq, said special forces Command spokesman Maj. Jim Gregory.

"You can't even put words to how devastating this would be," Gregory said.

Special Forces Command and Disney said they were assisting the family.

"Our deepest concerns are with the family," said the spokesman, Jacob DiPietre.

Walt Disney World reopened a roller coaster Friday after an inspection determined that nothing mechanical caused the death of a 12-year-old rider one day earlier.

"Walt Disney World engineers and ride system experts completed a thorough inspection of the attraction overnight and found it to be operating properly," the company said in a statement. "A representative from the state Bureau of Fair Rides Inspection observed the ride inspection and testing."

The boy's death is the latest in a string of tragedies at Walt Disney World in recent years. At least 15 people have died at Disney's theme parks in Florida and California since 1989, including some with pre-existing health conditions. Disney-MGM is among Disney's four Florida parks.

Most of the company's recent troubles have been over another ride Epcot's "Mission: Space," a rocketship attraction that simulates a flight to Mars.

Two people have died in the last year after going on the ride, which spins in a centrifuge that subjects riders to twice the normal force of gravity. Now Disney offers people an option to ride a tamer version of the ride that does not spin.

The availability of portable defibrillators at Walt Disney World became an issue earlier in June when a wrongful-death lawsuit was filed by the parents of a child who died last year after riding that Epcot ride.

Disney-MGM closed the Rock 'n' Roller Coaster on Thursday but said a preliminary investigation showed the ride was operating normally. The park's high-speed rides, including Rock 'n' Roller Coaster, display signs warning away people with critical medical conditions. The sheriff's office was investigating, and state park safety officials were also notified.

A Disney Web site description of the ride says: "Zoom from 0-60 mph with the force of a supersonic F-14, take in high-speed loops and turns synchronized to a specially recorded Aerosmith soundtrack." Rock 'n' Roller Coaster is the second-fastest ride at Disney, with maximum speeds of 57 mph, and riders must be at least 48 inches tall. It opened in July 1999.

Theme park consultants said the ride is relatively tame.

"As roller coasters go that is not considered an ultra, ultra high-thrill coaster," said Dennis Speigel, president of Cincinnati-based International Theme Park Services Inc. "It does have some high launch speeds, but it's more along the traditional lines of what roller coasters are today."

The Orlando Sentinel reported that at its peak, the Rock 'n' Roller Coaster produces a pressure on the body that is five times that of gravity, which is considered high but not unusual for these types of rides. But ride-safety consultant Ken Martin of Virginia told the paper that 5 G's is sufficient to cause some people to lose consciousness.

"Five G's, depending on the length [duration] of those G's, is pretty tough," Martin said.

The Associated Press contributed to this report.