Balloon pulmonary valvuloplasty is an established method in the treatment of congenital valvular pulmonary stenosis. Balloon valvuloplasty was performed by using one or two balloons in a total of 19 mongrel dogs. Cross sectional area ratio ranging 145-406% was used to compare the relative sizes of the pulmonary annulus and the balloon. Hemodynamic changes and cardiac damages in single and double balloon groups were analyzed. Survival time of double balloon group was longer than that of single balloon group (p<0.05) Increment of the right ventriclular systolic pressure in single balloon group (mean 38 mmHg)was greater than that in double balloon group (mean 87 mmHg) was greater than that in double balloon gourp (mean 41 mmHg) (p<0.05). The locations of trauma were mainly the right ventricular free wall, the main pulmonary artery, the anterior leaflet of the pulmonary valve and in a less degree, anterior wall of the right atrium, the right ventricular outflow tranct and the left pulmonary artery int he order of frequency. There were no significant differences in cardiac damages between single and double balloon groups(p<0.05) Major microscopic findigns were sloughing of the endotheliu, fibrin deposition, hemorrhae, localized myocardial infarction and so on. In conclusion, double balloon pulmonary valvuloplasty is superior to single balloon technique in survival time and hemodynamics. Therefore, double balloon technique is recommended for the pulmonary valvuloplasty.