ORLANDO, Fla. (AP) – A 4-year-old boy who died after riding a rocket-ship ride at Walt Disney World was killed by a heart condition that can be aggravated by physical or emotional stress, an autopsy said Tuesday.

Daudi Bamuwamye of Sellersville, Pa., died in June after riding “Mission: Space.”

The boy had a condition that caused an abnormal thickening of the heart and produced an irregular heartbeat, the autopsy revealed. People who suffer from the condition are at risk of sudden death throughout their lives, the medical examiner’s office said.

“This risk could be increased under physical or emotional stressful situations,” the office said in a statement. “This condition may also eventually lead to heart failure.”

Disney officials issued a statement saying their sympathies were with the boy’s family. “In regard to the reports, we believe they speak for themselves,” it said.

The $100 million Epcot ride, one of Disney World’s most popular, was closed after the death but reopened after company engineers concluded it was operating normally.

“Mission: Space” spins riders in a giant centrifuge that subjects them to twice the normal force of gravity, and it is so intense that some riders have been taken to the hospital with chest pain.

A warning sign posted last year reads: “For safety you should be in good health, and free from high blood pressure, heart, back or neck problems, motion sickness or other conditions that can be aggravated by this adventure.”

The autopsy said the boy apparently had the condition since birth, but it was unclear if his parents knew about it. Their lawyer, Robert Samartin, issued a brief statement but did not return calls.

“Mr. and Mrs. Bamuwamye and their daughter, Ruthie, remain crushed by this devastating loss. They would like to thank everyone for their continued thoughts and prayers,” Samartin said.

Meanwhile, a study released Tuesday at an American Heart Association conference in Dallas gave support to the notion that heart problems can be triggered or aggravated by roller coaster rides.

Researchers at the University Hospital of Mannheim in Germany put 55 healthy people on roller coaster rides and monitored their heart rates during the two-minute experience. Average heart rates rose from 89 beats per minute before the ride to 155 just afterward, with women’s rates rising significantly more than men’s.

These rates are high enough to trigger rhythm problems, and two participants experienced different types of them.

“We strongly recommend to people with heart disease not to ride a roller coaster,” said the study leader Dr. Jurgen Kuschyk, a cardiologist at University Hospital in Mannheim, Germany.