In the last few years, the pyridazine derivatives have been found to exhibit a wide range of pharmacological activities. A large number of research articles and patents described them, and several drugs based on its nucleus have come into light. Pyridazinone, a derivative of pyridazine, was initially exploited in search of cardiovascular drugs and for its use in agrochemicals, but later on this nucleus was found to be associated with plethora of activities. In this article, we have reviewed the influence of structural changes on the pharmacodynamic profile of the pyridazinone moiety.