In this chapter, obstructions to left heart inflow are considered in three broad categories: pulmonary vein obstruction, left atrial-level obstruction (cor triatriatum and supravalvar mitral ring), and left ventricular (LV) inflow obstruction (mitral stenosis and hypoplasia). All have similar hemodynamic and clinical consequences: elevation of pulmonary vascular resistance and limitation of left-heart output, with signs and symptoms of heart failure, accompanied by pulmonary hypertension and/or edema. With the exception of acquired mitral stenosis resulting from rheumatic fever, congenital forms of LV inflow obstruction are rare, with most occurring in association with other cardiac malformations. Isolated forms of LV inflow obstruction are very rare. Left ventricular inflow obstructions are among the most challenging cardiovascular conditions to recognize, evaluate, and manage, and despite great advances in diagnosis and treatment, they remain very significant sources of morbidity and mortality for patients. © 2012 Blackwell Publishing Ltd.