The present experimental study reports the beneficial effects of newly synthetized substances IIIq and IIIb in vivo. These aryloxyaminopropanol drugs have been shown to antagonize the contraction caused by calcium comparable to verapamil and flunarizine in the model of the isolated guinea pig terminal ileum. Effects of substances on both the incidence of arrhythmias during ischemia and the reperfusion period and mortality were investigated in the rat model ischemia-reperfusion injury. We can conclude that compound IIIq in a dose of 10(-6) mol/kg is effective in reducing the incidence of reperfusion-induced arrhythmias. Substance IIIb (10(-6) mol/kg) administered before ischemia was not able to suppress arrhythmias in the rat model of myocardial infarction and reperfusion.