The intense antifibrillatory and antiarrhythmic actions of GS 015, a derivative of the novel structure series of the 5-(beta-aminoacyl)-3-carbalkoxyamino-iminodibenzyles, are demonstrated on models of myocardial ischaemia: antifibrillatory action on the acute coronary occlusion in the conscious rat (1.0 mg/kg i.v.) and antiarrhythmic action on the two-step coronary ligature in the conscious dog according to Harris (2.0 mg/kg i.v. and 5.0 mg/kg orally). On the strength of the present results it is discussed that GS 015 is first of all suitable for influencing "early arrhythmias" with re-entry mechanism and only in the second line for taking an influence on "late arrhythmias" which arise from the occurrence of ectopic focuses. The substance seems suitable for preventing terminal arrhythmias in patients with ischaemic heart disease as well as for treating arrhythmias in the acute stage of myocardial infarction.