Fascinating rhythm: atrial fibrillation-the beat goes on.

We runners worry a lot about injuries. Run long enough, far enough, fast enough and something is sure to ache, break, swell, tear, twist, bleed, blister or grow arthritic. The usual suspects: feet, ankles, knees, hips, back. On the other hand, there are parts of our bodies we never expect to fail. We pride ourselves in our heart and our lungs. As runners pound out mile after mile, year after year wondering what part of our musculo-skeletal system will self-destruct next, we believe our exercise creates a heart and lungs that are indestructible.