A 9-year-old boy collapsed and died Tuesday night as he was walking to his Little League baseball game in Las Vegas.
Spencer Melvin was walking to the baseball field with his father and brother, who were his coaches.
"The hardest part was watching his father, try desperately to save Spencer's life," says witness Jennifer Riley told ABC News affiliate KTNV. "I was walking right by them when it happened. No one knew what was going on."
A statement on the Peccole Little League website said, "Medics and volunteers tried everything to save the child but were unable to revive him."
Dr. Barry Love, director of Pediatric Electrophysiology at Mount Sinai Medical Center, says that sudden death in apparently healthy children is rare, affecting about 3.4 of every 100,000 individuals.
"First off, it is not due to a 'heart attack' in the way that we commonly use the term to describe a condition in adults that results from a sudden blockage of flow to the heart muscle," said Love.
Love said the most common cause of sudden death is a condition called hypertrophic cardiomyopathy, and the second most common cause are abnormalities of the way the coronary arteries arise from the aorta.
"In this rare condition, there can be episodic spasm of this abnormal coronary artery leading to lack of blood to the heart. This condition is very difficult to detect especially in a previously asymptomatic individual," said Love.
Other conditions that can lead to sudden death are a weak heart muscle or electrical abnormalities of the heart, said Love.
Dr. Daphne Hsu, division chief of Pediatric Cardiology at The Children's Hospital at Montefiore Hospital, said Spencer could have suffered from ventricular tachycardia, an extremely rapid heartbeat.
"With ventricular tachycardia, the heart beats so fast that it cannot deliver enough oxygen to the brain and body and the child dies," said Hsu.
The cause of Spencer's death won't be known until an autopsy is performed.
The Peccole Little League is selling jersey patches in honor of Spencer, proceeds from which will go to his family to help pay for medical and funeral costs.