Take a Bullet for You — J.S. Frankel

Paul Rosen, seventeen, has led a short and unfulfilling life. Stricken with severe cardiomyopathy, his time is limited, and he knows it. Still, he does what he can in the time he's got. The course of his life changes when a little man named Cawthorne shoots him in the chest. In the hospital, Paul learns that a phantom bullet is circling his heart. Modern surgery can't help, and what's worse, Paul becomes a target of insect-like aliens, led by a thing called Sagras. The CIA then steps in, wanting the secrets of the aliens. Danger, thrills, and mayhem ensue, and finally, Paul, aware that his time is short, decides to go after Sagras and settle the matter once and for all—even if it costs Paul his life.