Purpose: To assess the cause of a "bite"-shaped signal void artifact often seen in 1.5 Tesla (T) and 3T gradient echo MR images in myocardium along the infero-apical border of the heart, MRI simulation was used to conduct experiments impossible in reality. Two previous studies attempting to explain the origin of this artifact came to different conclusions. One suggested deoxygenated blood in the posterior vein of the left ventricle (PVLV) leads to a susceptibility gradient that causes the artifact. The other suggested the difference in susceptibility between lung tissue and myocardium was responsible. This study assessed the relative effect of each possible cause. Materials and Methods: Anthropometric phantoms were developed for use with a previously reported MRI simulator. The images were simulated at 3T with gradient echo scans using TE = 4 ms, TR = 25 ms, and θ = 25°. Results: The simulations indicate that both susceptibility differences can lead to signal losses in the area of the artifact with contributions from the PVLV being more localized while lung tissue effects are stronger but more spatially distributed. Conclusion: The data support the conclusion that both differences together, rather than one or the other, are responsible for the artifact. © 2008 Wiley-Liss, Inc.