SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT) CARDIAC SCAN WITH 123I-MIBG AND MYOVIEW Single Photon Emission Computed Tomography (SPECT) cardiac scan with 123I-mIBG and Myoview will be used to measure cardiac sympathetic activity. The test will take approximately 5 hours with approximately 3.5 hours of break in the middle.