This invention relates to compounds of formula I;

and their use as antagonists of P2X3 and P2X2/3 receptor activity, pharmaceutical compositions comprising such compounds, and methods of treatment therewith. Compounds of the invention can be used for the treatment and/or prevention of pain and chronic pain and tolerance to analgesic, respiratory disorders and dysfunctions, and treatment of overactive bladder, bladder pain syndrome, dysuria and in general in genitourinary diseases, cardiovascular disorders and more in general for the potential treatment of visceral organ diseases and disorders characterized by the involvement of P2X3 and P2X2/3 receptors.