Figure 33-3 Color Doppler imaging of severe mitral stenosis. This four-chamber echocardiogram reveals a thickened and narrowed mitral valve (MV) indicative of mitral stenosis (MS). Color Doppler demonstrates (1) acceleration of blood flow into the stenotic valve (a light blue semicircular area immediately above the valve called "PISA"—proximal isovelocity surface area), (2) a narrow color jet across the valve itself, and (3) a 1 by 4-cm color jet extending from the undersurface of the valve into the left ventricle. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. (From Cahalan MK: Intraoperative Transesophageal Echocardiography. An Interactive Text and Atlas. New York, Churchill Livingstone, 1997.)