This paper reports on the initial performance evaluation of a small field-of-view, mobile PET/SPECT system for bedside imaging. The system was designed to move within a hospital to image patients who cannot easily be transported to a conventional PET or SPECT facility, for example, patients within an intensive care unit (ICU). The focus of the system is cardiac imaging in which both viability (18F fluorodeoxyglucose; FDG) and perfusion (99mTc Sestamibi) images are desired. This paper evaluates the capabilities of the mobile system for acquisitions at both 140 keV (Tc-99 m) and at 511 keV (F-18) operated in single photon counting mode. Parameters evaluated were the planar and reconstructed SPECT spatial resolution, the intrinsic energy resolution, sensitivity, and the count rate capability. Results demonstrate an intrinsic energy resolution of 32% at 140 keV and 23% at 511 keV, a planar intrinsic spatial resolution of 0.56 cm full width half-maximum (FWHM) at 140 keV and 0.61 cm FWHM at 511 keV, a system spatial resolution at 10 cm of 1.14 cm FWHM for both 140 keV and 511 keV, a reconstructed SPECT spatial resolution of 1.37 cm at 140 keV (22 cm radius-of-rotation), a sensitivity of 3.1 countsldrmuC-1ldrs-1 at 140 keV and 0.48 countsldrmuC-1ldrs-1 at 511 keV, and a maximum count rate of 1.46 times 105 counts/s at 140 keV and 1.56 times 105 counts/s at 511 keV.