Right-to-left shunting is usually associated with congenital conditions involving the heart, lungs, and the blood vessels that connect both organs. It is demonstrated by echocardiography, transesophageal ultrasound, CT scan, MRI and more definitively by conventional angiography. In this paper, we present a 16-year old female who manifested with progressive dyspnea, persistent cyanosis and decreased arterial oxygen saturation. Clinical assessment and arterial blood gas parameters suggested the presence of significant shunting. However, cardiac evaluation showed no intracardiac defects. High resolution CT scan of the chest with CT angiography of the pulmonary artery also showed no evidence of pulmonary vascular malformation or shunt anomaly. Lung perfusion scintigraphy performed after intravenous administration Tc99m-MAA showed tracer uptake in the brain, spleen and kidneys signifying the presence of a right-to-left shunt in the lungs. Cardiac catheterization later demonstrated the presence of primary pulmonary telangiectasia.