4-mono- and di-isobutylamino butanols of the formula (I): ##STR1## or a pharmaceutically acceptable salt thereof wherein R.sup.1 and R.sup.2 are the same or different and each is selected from the group consisting of hydrogen, halo, hydroxyl, alkyl of 1 to 4 carbon atoms and alkoxy of 1 to 4 carbon atoms and R is hydrogen or isobutyl, are useful for the treatment of circulatory disorders, particularly arrhythmias, in humans and animals.