Pompe disease 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 infants with severe cases of Pompe disease (called Classical Infantile Pompe disease), an excessive amount of glycogen accumulates and is stored in various tissues, especially heart, skeletal muscle, and liver, which prevents their normal function. This study being conducted to evaluate the safety and effectiveness of recombinant human acid alpha-glucosidase (rhGAA) as a potential enzyme replacement therapy for Pompe disease. Patients diagnosed with Classical Infantile Pompe disease who have a small, but inactive, amount of natural GAA enzyme present in their bodies (called Cross-Reacting Immunologic Material-Positive or "CRIM (+)" patients), will be studied.