Heterocyclic compounds of the formula: ##STR1## wherein the pyrroline ring and the symbols R.sub.1 and R.sub.2 together form an isoindoline, 6,7-dihydro-5H-pyrrolo-[3,4-b]pyrazine, 2,3,6,7-tetrahydro-5H-1,4-oxathiino-[2,3-c]pyrrole or 2,3,6,7-tetrahydro-5H-1,4-dithiino-[2,3-c]pyrrole nucleus, Het represents an optionally substituted pyrid-2-yl, quinol-2-yl or 1,8-naphthyridin-2-yl radical, Z represents oxygen or sulphur and R represents hydrogen, alkyl or halo-substituted alkyl, alkenyl, alkynyl, cycloalkyl, alkoxy, optionally substituted phenyl, phenylalkyl, the phenyl ring of which may optionally be substituted, phenylalkenyl, the phenyl ring of which may optionally be substituted, or R represents a 5- or 6-membered heterocyclic radical containing one or two hetero-atoms selected from nitrogen, oxygen and sulphur, and, when the pyrroline ring and the symbols R.sub.1 and R.sub.2 together form an isoindoline nucleus, the residue of the isoindoline nucleus represented by R.sub.1 and R.sub.2 may optionally be substituted, possess pharmacological properties, and are especially useful as tranquillizers, anti-convulsant agents, decontracturants and agents to produce hypnosis.