Heme is central to functions of many biologically important enzymes (hemoproteins). It is an assembly of four porphyrin rings joined through methylene bridges with a central Fe (II). Heme is present in all cells, and its synthesis and degradation balance its amount in the cell. The deregulations of heme networks and incorporation in hemoproteins lead to pathogenic state. This article addresses the detailed structure, biosynthesis, degradation, and transportation associated afflictions to heme. The article is followed by its roles in various diseased conditions where it is produced mainly as the cause of increased hemolysis. It manifests the symptoms in diseases as it is a pro-oxidant, pro-inflammatory and pro-hemolytic agent. We have also discussed the genetic defects that tampered with the biosynthesis, degradation, and transportation of heme. In addition, a brief about the largest hemoprotein group of enzymes- Cytochrome P450 (CYP450) has been discussed with its roles in drug metabolism.