This paper investigates the biological effect of intracardiac ultrasound irradiating myocardium in dogs.A ultrasound catheter was inserted into the dog's left ventricular chamber and the therapeutic ultrasound energy(1w/cm2,one minute)was delivered.The immediate change of myocardial pathobiology and microstructure were observed,meanwhile hemodynamics was measured.Compared with controls,mitochondria generally little swell,capillary endothelium cell also swell after the dogs were irradiated by ultrasound.In general,intracardiac ultrasound irradiating myocardium can enhance the permeability of capillary and myocardial cell membrane,which may be a new,safe and effective method for interventional ultrasound therapy of cardiovascular disease.