Pharmaceutical agent containing amino derivatives of 2-methyl-5-(2-hydroxystyryl)-1,3,4-thiadiazole

A therapeutic agent for blocking cardiac beta-1-receptors and for treating hypertonia and cardiac arrhythmias which comprises an effective amount of compound of the formula I ##STR6## where R is hydrogen, alkyl of 1 to 8 carbon atoms, which is unsubstituted or substituted by hydroxyl, alkoxy of 1 to 3 carbon atoms or cycloalkyl with 3 to 8 carbon atoms in the ring, alkenyl or alkynyl of 2 to 8 carbon atoms, or cycloalkyl or cycloalkenyl with 3 to 8 carbon atoms in the ring, the cycloalkyl rings being unsubstituted or mono- or di-substituted by alkyl of 1 to 3 carbon atoms, or an addition salt thereof with a physiologically acceptable acid, as the active ingredient, together with conventional excipients and diluents.