Even though the heme degradation pathway consists of only two reactions, it and its major enzyme (i.e. HO), nonetheless, impact other processes not only through the removal of excess heme, but also through the production of several metabolically active compounds. Thus CO and biliverdin along with reactive iron, Fe2, are the primordial products of this ancient, highly conserved reaction. That every component of the heme catabolic pathway is directly or indirectly related to other reactions involving oxygen or light is, perhaps, no accident of nature. That a fundamentally destructive event can be linked with a multiplicity of synthetic events and various biological effects, depending on the timing and location of the HO activity, is testament to the economy and the ultimate beauty of nature. Furthermore, the interaction of the heme catabolic pathway with that of the NOS system may lead to even more exciting avenues of research. It may be shown that the integrity of the heme catabolic pathway, which is ever present and plays a role in every tissue, is central to the existence of most complex organisms.