Compounds of the formula ##STR1## WHEREIN Ar.sub.1 and Ar.sub.2 denote an optionally substituted aromatic hydrocarbon radical or a monocyclic, monoazacyclic or diazacyclic radical of aromatic character and Alk represents lower alkylene, or salts thereof, exhibit .beta.-receptor-blocking, blood pressure-lowering and vasodilatory effects and are useful for example in the treatment of arrythmias and angina pectoris, and as blood pressure-lowering agents.