Structural and functional changes of pulmonary circulation related to pathophysiology of pulmonary arterial hypertension (PAH) remains to be fully elucidated. Angiographic visualization in in vivo animals provided a powerful tool for assessing the major indexes associated with the pathogenesis of PAH. In this study, we have exploited the full potential of synchrotron radiation (SR) microangiography to show the ability to visualize pulmonary hemodynamics in a closed-chest mouse. Male adult mice were anesthetized and cannulated with a customized 24-gauge catheter into the right ventricle via the jugular vein for administering iodine contrast agent. The microangiography was performed on the left lung. We measured dynamic changes in vessel diameter in response to acetylcholine (ACh) and acute exposure to hypoxic gas (10 O(2)). Moreover, the pulmonary transit time was estimated by the time of contrast agent circulating. We were able to visualize the pulmonary arteries from the left pulmonary artery (LPA) to the third generation of branching (ID <100 mum). ACh and acute hypoxia induced vascular responses chiefly in the second and third branching vessels rather than the LPA and the first branching vessels. The transit time was only 0.83 sec. These results demonstrate the effectiveness of SR for visualize the pulmonary circulation in a closed-chest mouse. Future studies using SR microangiography on specific gene-targeted knock-out and transgenic mice will provide new insights into the pathophysiology of pulmonary dysfunction and functional adaptation to survive in hypoxic condition.