Jessica Moncrieff was in the middle of a soccer scrimmage one May afternoon when she heard cries for help coming from a boys' baseball team that was practicing nearby. Justin McAfee had collapsed while rounding third base—and had stopped breathing. "I ran over," says Jessica, 14, "and could see his eyes rolling back. I was scared, but knew I had to save his life."

For the next seven minutes, the high school freshman from Meridian, Idaho, who had taken a babysitting CPR course the year before, pumped his chest with her hands and blew air into his mouth, supplying Justin with a steady flow of oxygen in the critical moments following a cardiac arrest. "She was doing some of the best CPR I've seen," says paramedic Jeremy Schabot, who soon arrived on the scene and helped resuscitate Justin with a defibrillator.

By the time Justin, also 14, was whisked to a nearby hospital, his heart was beating again. Justin was diagnosed with a faulty heart valve and was recently fitted with an implantable cardioverter defibrillator while awaiting surgery to correct the problem. As he looks back on that frightening day on the baseball field, he thinks of Jessica's heroic efforts with awe. "I could have died," says Justin, who met Jessica for pizza a week later and bought her a necklace and teddy bear in appreciation. "What Jessica did is amazing."

For more info on CPR classes, visit WWW.REDCROSS.ORG