WESLEY CHAPEL, Fla. (AP) – A 4-year-old boy collapsed and died after he wandered in front of a “pitch-back” net and was accidentally struck in the chest by a baseball thrown by another youth.

Cayden Huels was a victim of a sudden heart disturbance called “commotio cordis” – Latin for “heart commotion” – a cardiologist said. Commotio cordis happens from time to time, but seldom to such a young child.

The chest wall impact must be near the center of the heart, and there’s only a 1 percent or 2 percent chance of it happening at the precise moment when it can be deadly.

“It has to be a specific location and carefully timed in the cardiac cycle,” said Dr. Barry Maron, a cardiologist with the Minneapolis Heart Institute Foundation who has studied the phenomenon for a decade. “You have to be unlucky.”

Cayden died Thursday night. He had pulled away from his 12-year-old brother at a local park and stepped in front of the pitch-back net, which bounces a thrown ball back to the pitcher.

An autopsy Friday showed Cayden died of ventricular fibrillation caused by a blunt impact to the chest, said Harrison Cowan, a medical examiner’s investigator in Tampa. Fibrillation results in little or no blood being pumped.

Maron said commotio cordis doesn’t show up as a cause of death because the heart suffers no structural damage, but it can be diagnosed through anecdotal information. He has confirmed 200 cases but believes others might not have been reported or diagnosed.

The impact doesn’t have to be hard, Maron said. Little League balls generally are thrown 40 or 50 mph, but he said it doesn’t have to be that fast. While commotio cordis most often happens during sports, it can be caused by any projectile. Victims have been up to 45 years old. Maron said the fatality rate is 85 percent.

In September, 11-year-old Andy Buff suffered commotio cordis when he was struck in the chest by a pitched ball in Columbia, S.C. However, he was revived by two medical professionals who had sons playing in the same tournament, and he missed only one day of school.

Cayden’s family was too distraught to speak. “Cayden was their world,” said Charlie Van Auken, a colleague of Cayden’s father, Danny Huels, at Ricoh Americas Corp.

AP-ES-11-03-07 1857EDT