A patient with polysplenia syndrome, dextrocardia, left atrial isomerism, normal great vessel relationships, and no intracardiac shunts developed progressive cyanosis and clubbing. Pulmonary arteriovenous malformations (PAVMs) were diagnosed by angiography and confirmed by lung biopsy. Superior mesenteric arteriogram revealed hypoplasia of the intrahepatic portal vein branches and a portosystemic shunt. The possible etiologies of PAVMs are discussed.