March 4, 2011 -- Celebration turned to tragedy Thursday night at a Michigan high school when 16-year-old Wes Leonard collapsed on the basketball court and later died after scoring the game-winning shot in overtime, helping his team clinch a perfect season.

According to Dr. David A Start, the forensic pathologist and medical examiner of Ottawa County, the cause of death was cardiac arrest due to dilated cardiomyopathy -- an enlarged heart.

Leonard's game-winning layup, which earned two of his 21 points that game, led the undefeated Fennville Blackhawks to a 57-55 win over Bridgman High School. Teammates hoisted in him the air moments before he collapsed.

"He made the shot and then the game was over, we had won, everyone rushed the court," said Tobias Hutchins, a senior at Fennville High School who was at the standing-room-only game. "He did the team lineups where they all shake hands, the basketball team held him up, he started walking, then collapsed."

The gym went quiet as coaches and players surrounded Leonard, who was lying on his back.

"Nobody knew for sure why he had collapsed and was suddenly on the floor," said Tim Breed, a spokesperson for Holland Hospital who was also at the game.

Suspecting possible heat exhaustion, people tried to and cool Leonard down with ice packs while waiting for the ambulance.

"There was a sense of the crowd being stunned and just being shocked," Breed said. "Those who were obviously close to him there were those who were crying so many people on their cell phones just a sense of disbelief. We had gone from a monumental high one minute literally a minute or two minutes later to this hushed sense of shock."

Paramedics performed CPR and took Leonard to a defibrillator on the court. Soon after he was rushed by ambulance to nearby Holland Hospital, where he died two hours later at 10:40 p.m.

Sudden Death in Young Athletes

Sudden death in young athletes is relatively rare, but a major concern among schools and professional organizations. It gained significant attention in 1990 with the death of 23-year-old Hank Gathers, a basketball star at Loyola Marymount University.

Gathers died after collapsing on the court during a game against the University of California, Santa Barbara. A medical examiner determined that Gathers, suffered from hypertrophic cardiomyopathy -- an enlargement of the heart due to thickening of the muscle walls.

According to a 2003 review published in the New England Journal of Medicine, hypertrophic cardiomyopathy is the leading cause of sudden death among athletes, accounting for roughly a quarter of deaths.

Dilated cardiomyopathy was implicated in only 2.3 percent of athlete deaths.

What led to Leonard's condition, which prevents the heart from efficiently pumping blood to the rest of the body, is unknown. According to the National Institutes of health, risk factors include heart disease or a family history of it, high blood pressure, vitamin or mineral deficiency, infections involving the heart muscle, and the use of certain drugs or medications.

Thirty percent of dilated cardiomyopathy cases are inherited, according to Dr. Steven Fowler, a cardiac electrophysiologist at the Cardiovascular Genetics Program at NYU Langone Medical Center.

Symptoms, such as shortness of breath, rapid and irregular pulse, chest pain and faintness, are often subtle and develop slowly over time. But they can be severe and come on suddenly.

"Awareness about sudden cardiac death is critical," Fowler said, adding that 350,000 people die suddenly each year in the United States. "The people at most risk for sudden cardiac death often have the least amount of symptoms."

When detected, dilated cardiomyopathy can be treated using drugs that lower blood pressure or dilate the blood vessels. But screening tests that effectively detect so-called "silent" heart problems are limited. One reason for the dearth is the rarity of sudden death from all cardiovascular causes among young athletes. The prevalence, according to the NEJM review, is only 0.5 percent -- an infrequency that carries significant cost-benefit considerations.

Currently, most U.S. high school and college athletic programs require athletes to complete a health history questionnaire and undergo a physical exam before they can participate. But the quality of both has been the topic of scrutiny, according to the NEJM review.

"The guidelines examiners are given for screening high school athletes are inadequate in 40 percent of the states when measured against the recommendations of the American Heart Association," wrote Dr. Barry Maron, director of the Hypertrophic Cardiomyopathy Center at the Minneapolis Heart Institute Foundation. "Improvements in the screening process related to history taking and physical examination would undoubtedly result in the identification of greater numbers of athletes with previously undiagnosed but clinically relevant cardiovascular abnormalities."

Dr. Paul Thompson, director of cardiology and the athletes' heart program at Hartford Hospital in Connecticut, said it's unlikely that a routine physical exam would have picked up Leonard's condition.

"If there's a family history, it's detectable. If not, it's not," Thompson said. "We see people who felt totally fine, and then all of a sudden they get sick and their heart dilates up. It can happen very, very quickly. It comes out of the blue."

On Wednesday night, Leonard wrote on Facebook: "Got a good long shower ...ready for bed and game tomorrow!!!!!"

Sudden Death in Young Athletes

Last week Leonard had the flu and was recovering, his cousin Krys Leonard told ABC News.

"That's the classic story. Kid gets a bad case of the flu, they come back and they don't feel quite the same," Thompson said. "If he was screened at the start of season it might not have been detected. It can happen within two weeks."

Thompson said the flu can cause inflammation of the heart, called myocarditis, which can weaken the muscle walls leading to dilated cardiomyopathy.

Sudden death is not always the result of heart defects. Head and spine trauma, asthma and aneurysm are also reported. Last October, 26-year-old Fran Crippen died during a swimming race off the coast of Abu Dhabi, possibly due to heat stroke.

Another Fennville athlete, 14-year-old wrestler Nathaniel Hernandez, died in Jan. 2010 following a seizure.

Leonard was also quarterback for the Fennville football team, which won the Southwestern Athletic Conference North Division championship this season. Leonard threw seven touchdowns in the winning game, according to the Holland Sentinel.

Larry Gilbert, coach of one of Fennville's biggest competitors, Gobles High School, said Leonard's goal was to be a Division 1 athlete.

"And he took care of his body, he worked out he knew what he had to do," said Gilbert, who couldn't believe the news. "When I coached against him I was trying to figure out to stop him but it was so exciting to see him play I'd have to keep my thoughts together to not get too wrapped up in watching him play."

Leonard's mom, Jocelyn Leonard, was the Fennville High School choir teacher. His younger brother, who is in eighth grade, plays basketball too and was looking forward to joining the Fennville Blackhawks.

"He was hoping he'd get pulled up to varsity and play with his brother during his senior year," said Gilbert. "It breaks my heart."

Teammates and friends gathered at a church at midnight to remember Leonard, who was "pretty much friends with everybody," according to Hutchins.

Leonard's girlfriend of two and a half years, Selena Beltran-Peña, wrote on Facebook: "Not a day will go by that i won't think about you & your smile. I know your watching over all of us babe..I can officially say you are my angel. Even though I knew it before. I love you forever & always. rest in peace."