BACKGROUND: In congenital heart disease, the lung perfusion through stenosed pulmonary artery is usually decreased. And this decrement of lung perfusion also occurs with diaphragmatic palsy after the operation of congenital heart disease. It is difficult to delineate the amount of lung perfusion in case of combination of pulmonary artery stenosis and diaphragmatic palsy. We examined the change of lung perfusion after the induction of diaphragmatic palsy in rabbits. METHODS: We dissected left phrenic nerves in 20 rabbits to induce left diaphragmatic palsy. The lung perfusion scan was performed with 99mTc-MAA and the movement of diaphragm was examined with fluoroscopy. They were performed as baseline data and on 3rd and 10th day postoperatively. The amount of left lung pefusion before and after diaphragmatic palsy was compared and analysed in 12 rabbits which definitely had diaphragmatic palsy. RESULTS: Weight of the rabbits was 1.65+/-0.26 kg. Left lung perfusion percent was 45.93+/-6.42% before operation and these were 32.48+/-6.09% and 37.62+/-3.39% on the 3rd and 10th postoperative day, respectively. Left lung perfusion was significantly decreased just after diaphragmatic palsy but it was not changed thereafter. The decrement of lung perfusion was not affected by the body weight. The decreased amount of left lung perfusion was reciprocally correlated with the body weight of the rabbits on the postoperative 3rd day but not 10th day. CONCLUSION: Left lung perfusion percent of the rabbits was decreased 7% with the induction of diaphragmatic palsy and the decreased amount was reciprocally correlated with the body weight just after the diaphragmatic palsy was induced.