FENNVILLE, Mich. — In a heartbeat, he was gone.

High-school basketball hero Wes Leonard had just made the game-winning shot in overtime on home court to close his team’s perfect season Thursday night — triggering a wild roar from the stands in the Fennville HS gym.

The 16-year-old’s mom, Jocelyn, and dad, Gary, watched with pride from the stands as their eldest boy — his face flush with victory — was hoisted to his teammates’ shoulders.

But the noise became a shocked hush when the teen collapsed in a heap, his face deathly pale, his chest still.

“We were all picking up Wes, and then we let him go and he just fell,” recalled teammate Jordan Vander Bok, 16.

Almost immediately, Gary Leonard was at his boy’s side.

“Come on, Wes, breathe!” he screamed, recalled Tony Pena, whose daughter, Selena, was dating Wes.

Less than two hours later, the star athlete — who had an undiagnosed enlarged heart — was pronounced dead at nearby Holland Hospital. A defibrillator at the gym was never used.

“When that doctor told us Wes didn’t make it, there was a hundred people [in the emergency room] that just dropped,” Pena said. “He was one of the biggest, strongest kids you will ever know.”

The young athlete’s winning basket ensured the team a 20-0 finish for the season for the first time in at least 20 years.

His death has ripped this town’s heart out.

“Wes Leonard was the quintessential all-American kid,” said Fennville School Superintendent Dirk Weeldreyer.

“He had a great grin and was always cheerful. Younger kids throughout the community looked up to him and idolized him.”

Within hours, memorial pages popped up on Facebook.

“I know your watching over all of us babe. I can officially say you are my angel. Even though I knew it before,” girlfriend Selena Beltran-Pena wrote on one.

Yesterday, Wes’ teammates gathered to mourn their unassuming star.

“If anything, we made fun of Wes,” Vander Bok joked. “Just the way he says things, it’s funny. He always said ‘duu’ instead of ‘dude.’ ”

Last night, relatives were too distraught to comment, as friends stopped by to be with the teen’s parents and younger brother.

Additional reporting by Cathy Burke in New York