After the autopsy, when the doctor found white blossoms of scar tissue on Wes Leonard's heart, he guessed they had been secretly building there for several months. That would mean Wes's heart was slowly breaking throughout the Fennville Blackhawks' 2010--11 regular season, when he led them in scoring and the team won 20 games without a loss.

It would mean his heart was already moving toward electrical meltdown in December, when he scored 26 on Decatur with that big left shoulder clearing a path to the hoop. It would mean his heart swelled and weakened all through January (25 against Hopkins, 33 against Martin) even as it pumped enough blood to fill at least 10 swimming pools.

This heart pounded two million times in February, probably more, heaving under its own weight, propelling Wes's 6'2", 230-pound frame along the glimmering hardwood with such precision and force that finally a kid from Hartford gave up on the rules and tackled him in the lane. By March 3, the night of Wes's last and most glorious game, his heart weighed 21½ ounces, double the weight of a normal heart, and it gave him all he needed from the opening tip to the final buzzer. Then the wiring failed, the current going as jagged as a thunderbolt, and Wes fell to the floor with his big heart quivering.

If all this seems implausible—that Wes could play so well for so long with such faulty equipment—consider a scientific phenomenon called functional reserve. The human heart has a reservoir of unused ability, like a powerful car that can go 150 mph but never gets pushed above 75. A normal heart will pump about 60% of its blood volume with each beat. But one cardiologist tells the story of a bodybuilder who thrived for nearly a decade with a heart that could pump only about 10% per beat. Pistol Pete Maravich, arguably the greatest college basketball player of all time, was born with no left coronary artery. His right one worked twice as hard. It kept him alive for 40 years. The body finds a w...