Pompe disease (also known as glycogen storage disease type II) is caused by a deficiency of a critical enzyme in the body called acid alpha-glucosidase (GAA). Normally, GAA is used by the body's cells to break down glycogen (a stored form of sugar) within specialized structures called lysosomes. In patients with Pompe disease, an excessive amount of glycogen accumulates and is stored in various tissues, especially heart and skeletal muscle, which prevents their normal function. The overall objective of this study is to evaluate the long-term safety and efficacy of Myozyme treatment in patients with infantile-onset Pompe disease.