Cor tria- triatum sinister is usually associated with other congen- ital malformations, specifically ASD, VSD, or anomalous pulmonary venous connection (partial or total).S4.2.1-1 The left atrial appendage is invariably in the same chamber as the mitral valve, separated from the pulmo- nary veins by the membrane. Supravalvular mitral steno- sis is typically caused by a fibrous ring on the atrial side of the mitral valve, separating the mitral valve from both the left atrial appendage and the pulmonary veins. The finding will have similar physiology to cor triatriatum and similar indications for intervention. It can be associated with an abnormal mitral valve that may also require in- tervention. Supravalvular mitral stenosis often comprises one part of a more complex sequence of serial left-sided inflow and outflow obstructions (ie, Shone complex). See Section 3.3 for recommendations on who should perform surgeries, cardiac catheterization, and other procedures in these patients; and Section 3.4 for recommendations on diagnostic evaluation. Recommendation-Specific Supportive Text 1. Cor triatriatum sinister is a membrane spanning the left atrium. Surgery has been largely success- ful with relatively few early or late deaths, which are usually attributable to associated congenital The gradient across the de- fect at the time of surgery was at least 8 mm Hg (mean 17 mm Hg; range 8 to 40 mm Hg).S4.2.1-3 After repair, recurrence of stenosis is not ex- pected. Although pulmonary vein stenosis has been demonstrated before and after surgery,S4.2.1-2 it is not usually progressive over time and has not been associated with PAH. 2. Pulmonary venous stenosis has been demon- strated before and after surgery, but it is not usually progressive over time and has not been associated with PAH. 3. 