A heme oxygen binding behavior was described through a unique geometric and electronic comparison of zinc porphyrin complexes. In this work, a charge transfer model for saddled metalloporphyrin complexes outlined the push effects of the ring nonplanarity and axial imidazole, and the pull effect of the axial dioxygen. The origin and role of the horizontal (ring nonplanarity) push effect and its relationship to the vertical (axial ligand) push/pull effect and its contribution to dioxygen binding were considered from the perspectives of crystal structures, theoretical calculations, and bathochromic shifts. Single-point energy and molecular orbital calculations starting from crystal structures were used to obtain the electronic structures of zinc porphyrin complexes. This study not only revealed that the electronic behavior of metalloporphyrins is driven by ring nonplanarity and axial ligation but also afforded new insight into the oxygen carrier mechanism in heme.