The efficacy of endovascular irradiation of the blood with He-Ne laser by the method developed by the authors was examined in 295 patients with primary acute transmural myocardial infarction. Laser therapy was conducive to effective alleviation of the pain syndrome and prevention of anginous status. Twenty-four-hour Holter monitoring, carried out before and after irradiation, has detected high antiarrhythmic activity in respect of complex ventricular arrhythmias and a preventive possibility of fibrillations. Studies of precardial ECG parameters and measurements of the blood enzymic activities (creatine phosphokinase and MB creatine phosphokinase) have shown that irradiation carried out within the first hours of myocardial infarction is conducive to limitation of the infarction area, i.e. that endovascular laser therapy is a highly effective and pathogenetic method for acute myocardial infarction treatment.