A 22-year-old male presented with recurrent stroke, central cyanosis, and dyspnea. Transesophageal echocardiography and cardiac catheterization revealed bidirectional shunt flow through atrial septal defect (ASD) without pulmonary arterial hypertension. The orifice of inferior vena cava facing towards ASD opening led partially right to left shunt resulting in cyanosis with normal pulmonary arte...

Cyanosis is defined by bluish discoloration of the skin and mucosa. It is a clinical manifestation of desaturation of arterial or capillary blood and may indicate serious hemodynamic abnormality. The goal of this article is to help the reader understand the etiology and pathophysiology of cyanosis and to formulate an approach to its differential diagnosis.

Methemoglobin is a type of hemoglobin in which the ferrous ion has been oxidized to the ferric state. It is therefore incapable of combining with or transporting the oxygen molecule, which is replaced by a hydroxyl radical. Methemoglobinemia can be acquired or inherited. Most cases are acquired and are primarily due to exposure to certain drugs and chemicals, such as nitrates, nitrites, quinone...