Abstract: The invention relates to new aminoguanidine derivatives of the general formula (I), ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 each represent hydrogen or halogen atom, C.sub.1-4 alkyl, nitro, trifluoromethyl or C.sub.1-4 alkoxy group,R.sup.4 and R.sup.5 represent a C.sub.1-4 alkyl group, furthermore NR.sup.4 R.sup.5 may form a 5 to 7 membered saturated heterocyclic group containing either one or two nitrogen atoms or a nitrogen and an oxygen atom and being optionally substituted by one or two methyl, hydroxymethyl or hydroxyethyl groups,R.sup.6 and R.sup.7 each represent a hydrogen atom, normal or branched C.sub.1-4 alkyl or C.sub.2-4 alkenyl group,and to their pharmaceutically acceptable acid addition salts as well as to a process for the preparation thereof.The new compounds of the invention possess valuable antiarrhythmic activity and are devoid of the undesired circulatory side effects of the known antiarrhythmic compounds.