Patent ductus arteriosus(PDA) is one of the most common conditions in patient with continuous murmurs, but it often confused with other conditions such as arteriovenous fistula at various sites. We experienced a case of PDA in adult that could not definitely diagnosed by echocardiography, but confirmed by passage of the catheter from descending thoracic aorta far distal to the origin of subclavian artery to main pulmonary artery. A 28-year-old man admitted for evaluation of continuous precordial murmurs. Transthoracic echocardiography revealed small continuous flow at perivalvular area of pulmonic valve which did not match a typical finding of PDA. Transesophageal echocardiography did not provide additional informations. Coronary angiogram to exclude coronary arteriovenous fistula did not find any abnormalities. Oxymetric data by cardiac catheterization revealed 6.6% oxygen step-up from right ventricle to main pulmonary artery. Calculated Qp/Qs was 1.9. Thoracic aortogram showed opacification of pulmonary artery, but could not define the precise site and size of shunt. Diagnostic confirmation was maden by end-hole catheter that was introduced to thoracic aorta and then passed into main pulmonary artery at much lower level than that of typical PDA. So we performed transcatheter closure of PDA using Amplatzer duct occluder(AGA medical corporation). Size of Amplatzer duct occluder(8/6 mm) was carefully determined by selective angiogram and deployment of the device was successfully done. Final thoracic aortogram 10 min after the procedure revealed no opacification of pulmonary artery and continuous murmur disappeared. The patient discharged without complaint and complication.