We studied the effects of heme distortions on the chemical properties in two protein classes, oxidoreductases and oxygen carrier proteins, in the Protein Data Bank by a combination of statistics and quantum chemistry. A statistical analysis of heme distortion provided the characteristic distortions. They were reasonably correlated with the redox potentials and oxygen affinities evaluated by quantum chemical calculations, implying that heme proteins utilize these distortions to enhance their functions. The combination of statistical analysis and quantum chemical calculations is useful for the elucidation of the structure-function relationships.