Left-sided congestive heart failure in the horse is a common squelea to degenerative valvular disease and can potentially be life threatening. Abnormalities of the atrioventricular valve (AV) can lead to insufficiency and mitral regurgitation. In the horse, valvular degeneration is the most common etiology for AV valve pathology. Mean survival time is based on several factors including the degree of mitral regurgitation and the presence of a ruptured chordae tendinae. The end result leads to a decrease in cardiac output and pulmonary edema from increased pulmonary pressure. This case study will highlight a 14-year-old Thoroughbred gelding with an acute onset of frothy nasal discharge. The history, physical examination findings, pathophysiology, etiologies, diagnostics, therapeutics, and prognoses for patients with acute pulmonary edema resulting from mitral insufficiency are discussed.