Recurrence and progression of the various asso- ciated lesions are expected, subsequent surger- ies are common, and mortality may be associated with other defects.S4.2.2-2 Therefore, these patients require follow-up at a center where such abnor- malities can be followed and future interventions considered. Choices and techniques for valve re- pair or replacement are based on consideration of coexisting abnormalities including the likelihood of future surgery. CLINICAL STATEMENTS AND GUIDELINES 4.2.3. Subaortic Stenosis Recommendations for Subaortic Stenosis Referenced studies that support recommendations are summarized in Online Data Supplement 33. COR LOE Recommendations Diagnostic IIb C-LD Stress testing for adults with LVOT obstruction to determine exercise capacity, symptoms, electrocardiographic changes, or arrhythmias may be reasonable in the presence of otherwise equivocal indications Therapeutic I C-EO Surgical intervention is recommended for adults with subAS, a maximum gradient 50 mm Hg or more and symptoms attributable to the subAS. I C-LD Surgical intervention is recommended for adults with subAS and less than 50 mm Hg maximum gradient and HF or ischemic symptoms, and/or LV systolic dysfunction attributable to subAS.S4.2.3-3 IIb C-LD To prevent the progression of AR, surgical intervention may be considered for asymptomatic adults with subAS and at least mild AR and a maximum gradient of 50 mm Hg or more.S4.2.3-4 S4.2.3-6 Synopsis SubAS may occur as a discrete membrane below the aortic valve in the LVOT, as a longer tunnel-like obstruc- tion, as a consequence of chordal attachments in pa- tients with abnormalities such as AVSD, or because of surgical repairs involving VSD baffled to a transposed aorta, such as seen in the Rastelli operation. SubAS may occur in isolation or as part of a suite of abnormalities. 