Expander-based breast reconstruction is a popular form of post-mastectomy reconstruction and involves the temporary subcutaneous implantation of breast tissue expanders that require periodic, incremental inflation with sterile saline by injection until the desired amount of tissue is developed. One type of tissue expander injection port system currently on the market is made of titanium and rare-earth magnets that enhance injection accuracy. These highly dense metallic materials, however, can cause attenuation artefacts on multiple gated acquisition cardiac studies. In this report, we present the cases of two breast cancer patients with artefacts on multiple gated acquisition scans, characteristic of these tissue breast expanders.