The present invention provided pyrrolobenzimidazoles or tautomer thereof, of the general formula: ##STR1## wherein R.sub.1 is hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.6 alkenyl or C.sub.3 -C.sub.7 cycloalkyl;R.sub.2 is hydrogen, cyano, C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.6 alkenyl, or a carbonyl group substituted by hydroxyl, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkyoxy, amino, C.sub.1 -C.sub.6 alkylamino, C.sub.2 -C.sub.12 dialkylamino or hydrazino, orR.sub.2 and R.sub.1 together with the carbon to which they are attached form a C.sub.3 -C.sub.8 spirocycloalkyl ring, or R.sub.1 and R.sub.2 together form C.sub.3 -C.sub.7 alkylidene or C.sub.3 -C.sub.7 cycloalkylkidene,X is a valency bond, C.sub.1 -C.sub.4 alkylene or vinylene andT is oxygen or sulphur;and Het is furanyl, thienyl, pyrrolyl, pyrazolyl, imidazolyl, oxazolyl, thiazolyl, triazolyl, oxadiazolyl, thiadiazolyl, pyrazinyl, pyrimidinyl or pyridazinyl wherein the heterocyclic five- and six-membered rings are unsubstituted or substituted by one or more C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, hydroxyl, oxo, nitro, amino, halo, carboxyl, C.sub.2 -C.sub.7 alkoxycarbonyl, aminocarbonyl or cyano groups; or a physiologically acceptable salt thereof with an inorganic or organic acid. These compounds are useful for treating heart or circulatory diseases, especially those which respond to a change of blood pressure, an increase in cardiac output and/or a change in micro-circulation.