A 44-year-old man with pulmonary sarcoma presented symptoms of dyspnea, cough, chest pain, and fatigue. During echocardiographic examination, a large mass was revealed inside the left atrium causing severe mitral valve obstruction. The patient underwent chemotherapy with alleviation of symptoms. Follow-up echocardiogram revealed decreased mass size and no mitral valve obstruction. The mass stemmed from the left posterior pulmonary vein. After surgical resection, the mass was revealed to be a sarcoma. Postsurgery echocardiogram was normal. The patient has remained asymptomatic. Chemotherapy may decrease the size of a cardiac sarcoma and alleviate mitral valve obstruction symptoms, thus facilitating complete resection.