BACKGROUND Unilateral cardiogenic pulmonary edema is a rare disease. A common cause is mitral valve and asymmetrical blood regurgitation that is primarily directed toward the upper right pulmonary vein, causing mean capillary pressure to increase on the right side and leading to right pulmonary edema. METHODS A 41-year-old man was diagnosed with pneumonia after presenting with a 2-day history of cough and shortness of breath. Computed tomography indicated right pulmonary edema. He was managed with noninvasive ventilation; however, his condition continued to deteriorate, and he was transferred to the intensive care unit after tracheal intubation. METHODS Acute posterior mitral valve prolapses; unilateral cardiogenic pulmonary edema. METHODS Emergency mitral valve replacement was performed. During the operation, 2 ruptures of the chordae tendineae in the P2 scallop of the posterior mitral valve were found, and a No. 29 St. Jude mechanical mitral valve was implanted. RESULTS Cardiotonic and diuretic drugs were administered postoperatively. Tracheal intubation was removed on day 7; the patient was transferred to the general ward on day 11 and discharged on day 23 postoperatively. CONCLUSIONS Unilateral cardiogenic pulmonary edema is easily misdiagnosed. Computed tomographic (CT) imaging presentation, brain natriuretic peptide, and cardiac color Doppler ultrasound can assist in determining a differential diagnosis. Early surgical treatment is recommended for patients with acute mitral valve prolapse.