Novel 1-heterocyclyloxy- or 1-aryloxy-3-amido-alkylamino-2-propanol derivatives, processes for their manufacture, pharmaceutical compositions containing them and methods of using them in the treatment of heart diseases. The compounds possess .beta.-adrenergic blocking activity. Representative of the compounds disclosed is 1-(4-indolyloxy)-3-.beta.-isobutyramidoethylamino-2-propanol.