Myocardial perfusion imaging (MPI) is a valuable diagnostic tool for the diagnosis of coronary artery disease (CAD) and is susceptible to a variety of artifacts, which degrade image quality and decrease diagnostic accuracy. Pitfalls and Artifacts in nuclear medicine imaging are not rare and could be classified into issues related to patients, equipment, and technologist. One of these artifacts is unstable PMT gain, which is rare and related to equipment. It is crucial for nuclear physicians to be aware of potential artifacts and their potential effect on image quality. This knowledge helps them to prevent or correct these artifacts if possible and if not, consider the potential effect of these artifacts on image pattern and quality. Some of these artifacts are preventable by routine quality control procedures, but some other artifacts may occur regarding quality control procedures. Three different female subjects 55, 57, and 61 years old with a history of atypical chest pain were referred to our department for myocardial perfusion imaging. MPI was performed according to standard protocols and stress, and rest phases were done. These three cases had different patterns of perfusion abnormalities due to interruption of count detection for a few seconds in some frames during acquisition that was due to voltage drop that leads to unstable PM tube gain. Systematic errors due to voltage drops are not common, and they are not routinely sort of suspicion to artifactual perfusion abnormalities but they may cause misinterpretation of reports of MPI, and we should be aware of them.