Abstract: The substituted theophyllines of the formula: ##STR1## (wherein R.sup.1, R.sup.2 and R.sup.3, which may be the same or different, each represent alkyl of 1 to 6 carbon atoms, cycloalkyl of 3 to 7 carbon atoms, phenyl or phenylalkyl of 7 to 10 carbon atoms, each of which may be unsubstituted or substituted by one or more hydroxy groups, alkoxy or alkylthio groups of 1 to 4 carbon atoms, halogen atoms, cyano groups, nitro groups, carboxy groups, alkoxycarbonyl groups of 2 to 5 carbon atoms, amino groups, alkylamino groups of 1 to 4 carbon atoms or dialkylamino groups of 2 to 8 carbon atoms, or when the group is phenyl or phenylalkyl, by one or more alkyl groups of 1 to 4 carbon atoms;or R.sup.2 and R.sup.3 together represent a hydrocarbon chain of 3 to 6 carbon atoms optionally interrupted by a heteroatom;and n represents an integer of from 1 to 6)and the acid additional salts thereof, are novel compounds which are useful in the treatment of cardiac disorders.