SPECT-CT is an imaging method for diagnosing diseases and studying physiology of the body. In this type of imaging, due to the use of radiopharmaceutical for imaging (SPECT) and X-rays (CT), a relatively high dose of radiation is introduced into the patient. If the patient is pregnant, considering that the developing fetus is sensitive to any radiation in the uterus throughout the entire period before birth, there may be harmful and irreversible effects on the fetus; therefore protecting the pregnant woman and the fetus against radiation is of great importance. The purpose of this study is to evaluate and calculate the fetus absorption dose in cardiac imaging using the SPECT-CT machine in stress and resting conditions of the cardiac by injecting 20 mCi of radiopharmaceutical of 99m Tc-MIBI. X-rays are also emitted during CT imaging with 140 keV energy in 5 seconds. For this purpose, the Monte Carlo method, using the MCNPX code and the ORNL phantom, was applied to simulate the fetus in three, six and nine months of pregnancy, and the radiation absorbed doses of fetus absorption were calculated in three condition of stress and rest mode with two times urination, and resting mode without urination. The absorbed dose of fetus in stressed state in three, six and nine months of gestational age are 1.26 × 10 -2 , 2.9 × 10 -3 , 2.83 × 10 -4 mGy respectively. The fetus absorption dose in rest mode with two times urination in three, six and nine months of gestational age are1.84 × 10 -2 , 4.23 × 10 -3 , 4.14 × 10 -4 mGy respectively, and the fetus-absorbed dose in resting mode without urination, in three, six and nine months of gestation are 2.52 × 10 -2 , 5.79 × 10 -3 , 5.68 × 10 -4 mGy respectively. The results of this study indicate that the highest embryo absorption dose is related to cardiac resting imaging at the third month of the fetus. The fetus absorption dose has been calculated to be less than 0.05 Gy for all maintenance periods, which, according to the NCRP 128 and ICRP 84, do not cause a serious risk to the fetus. However, special immunological advices should also be given to pregnant women to reduce the absorption of fetus, especially in the early months of pregnancy.