Magnetic Resonance Imaging (MRI) of the heart and breathing muscles, special breathing tests (called pulmonary function testing), special exercise tests (using a stationary bike), and possibly an echocardiogram (ultrasound of the heart, commonly known as an "echo") will be completed up to 4 times per year for up to 4 years. Most participants will complete testing once or twice each year; however, some participants will be asked to repeat some of the tests twice during each visit.