A 28-year-old patient complains of periodic compressing heart pain. His brother died at the age of 34 from a cardiac disease with similar symptoms. Objectively: the patients skin is pale. Heart borders display no significant deviations. Heart sounds are loud, there is a systolic murmur above all the points with a peak above the aorta. Echocardioscopy reveals thickening of the interventricular septum in the basal parts, reduction of left ventricular cavity. What drug should be administered in order to prevent the disease progression?