This invention is to provide quinazolinone derivatives, and their acid salts and quaternary ammonium salts, having an effect of preventing or treating diseases caused by calcium ion overload in cells, such as ischemic heart disease, ischemic cerebral disease and ischemic renal disease, and their usage. The quinazolinone derivatives are represented by the formula: ##STR1## typically, T represents an oxygen atom; Y represents a phenyl or cyclohexyl group; R.sup.1 represents a hydrogen or chlorine atom; R.sup.2 represents a hydrogen atom; ring W represents a benzene or pyridine ring; Z represents a group of the formula: ##STR2##