To date, myocardial perfusion (MP) has been utilized to assess the adequacy of blood flow to the myocardium in order to determine the ischemic heart diseases. With the advent of SPECT/CT, MP became the most common investigation in the field of nuclear cardiology with more accuracy and details. Thallium-201 and Technetium-99m (Tc-99m) have been early used in cardiac nuclear imaging. Half-life of Tc-99m is 6 h, and its energy is 140 keV, while the half-life of Tl-201 is as longer as 73 h, its X-ray energies range between 69 and 81 kV in addition to gamma rays of 135 keV and 167 keV. The purpose of the present study was to explore the radiation dose rates emitted from the patients following Tc-99m sestamibi injection. To achieve that, the radiation emanated to the environment was measured at different distances from patients and various time intervals for 20 patients using GM counter. The mean radioactivity administered to the patients was 391.1 MBq (10.6 mCi), with a range between 276.8 MBq to maximum of 515.4 MBq. Radiation dose rate was found 9.07 mu Sv h(-1) at 1 m distance from the patient's chest level after 7.6 min, then decayed to 7.93 mu Sv h(-1) after 36.5 min, and 7.83 mu Sv h(-1) later to 66.4 min. It was concluded that 1 m distance from the patients sounds sensibly adequate to maintain the occupational dose within the safe limit following Tc-99m sestamibi injection, while verification of public dose rate <= 1 mu Sv h(-1) at 1 m distance from the patient prolongs to 14 h following Tc-99m injection.