After the qualifying tests, participants will return for the first of two separate imaging days that will include the same tests. The second imaging day will occur at the end of the medication period, approximately 2 months after the first imaging day. The first tests will be a whole body metabolism study and a heart metabolism imaging study, performed simultaneously. The whole body metabolism study will involve the injection of two tracers of metabolism, one for glucose and one for fatty acids. The heart metabolism imaging study will involve a positron-emission tomographic (PET) scan to take pictures of the heart and will include blood draws. The final imaging test will be a resting echocardiogram (ECHO) to measure heart function.