Objective   To establish the safety of a novel ultrasound catheter system that can increase gene expression by delivering transendocardial and intracardiac ultrasound irradiation.    Methods   An intracardiac ultrasound (US)irradiation catheter was placed in the left ventricle of living dogs. Enhanced green fluorescence protein plasmids (EGFP) were injected into myocardium through a special miniature needle in the catheter. Twelve health hybrid dogs at the age of 12 months

weighing 15-20 kg

were divided into EGFP+US group and EGFP group. Dogs in EGFP+US group were injected with 500 μg EGFP and then underwent intracardiac US irradiation for 1 min (1 MHz，1 W/cm). Dogs in EGFP group were injected with the same amount of EGFP. CK secretion was measured before，during and after irradiation. mRNA and protein expressions of EGFP in myocardium

liver

kidney and lung were detected on day 7 after irradiation to observe changes in their pathological morphology.    Results   EGFP were successfully injected into myocardium though an intracardiac US irradiation catheter. The mRNA and protein expression levels of EGFP were 6.5-fold and 3.4-fold higher in EGFP+US group than in EGFP group after irradiation (P0.01). No injury

hemorrhage

and CK secretion were observed in myocardium after irradiation. No change occurred in morphology of myocardium

liver

kidney and lung. No expression and deposition of EGFP were detected out of myocardium.    Conclusion    Intracardiac US irradiation is a safe and effective procedure for increasing the expression of naked EGFP in myocardial tissue of living dogs with no toxic and side effects.