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©2013 UpToDate ® Print Email Two-dimensional transthoracic echocardiogram (2D TTE) from the suprasternal notch view showing the right pulmonary artery Imaging the transverse aortic arch (TAo) from the suprasternal notch should be a standard part of every echocardiographic examination; the right pulmonary artery (RPA) can be viewed and when compared to the diameter of the transverse aortic arch, provides valuable information about the differential diagnosis of right ventricular enlargement. In panel A, the patient had a small ventricular septal defect and borderline normal right ventricular size on echocardiography; the RPA is smaller than the TAo, indicating a very small left-to-right shunt. In panel B, the patient had an Ebstein's anomaly of the tricuspid valve, the large right atrium is associated with a smaller than normal RPA, confirming the reduced pulmonary flow resulting from decreased functional volume of the right ventricle, tricuspid regurgitation, and right-to-left shunt across the atrial septum. In panel C, the patient had an atrial septal defect; the RPA is considerably enlarged, confirming that the ASD is likely to be associated with a large left-to-right shunt.