<qa>  What is important to know if the pacemaker or problems from dilated cardiomyThe hearts of children grow fast. It is important to be able to know if the pacemaker or problems from dilated cardiomyopathy are causing any changes in the heart that might cause problems. We expect to be able to use information we learn from this study to improve how we use pacemakers in the future to avoid problems that can happen over time. 