1. Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas 75231;
2. Department of Radiology, Mary Nell and Ralph B. Rogers Magnetic Resonance Center, University of Texas Southwestern Medical Center, Dallas 75235-9085;
3. Division of Cardiology, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235-8573; and
4. Department of Veterans Affairs Medical Center, Dallas, Texas 75216