We present a rare case of malignant pheochromocytoma in the left atrium and its surgical treatment. The patient was a 39-year-old male who presented a low-grade fever with perspiration. A large tumor was first detected in the left atrium by chest CT, and was confirmed by ultrasonic echo cardiogram and chest MRI. A left adrenal tumor was indicated also by abdominal echography. To prevent the risk of its embolization, surgical excision was performed on a subemergency basis. The patient developed near Shock State on the operative day, presumably due to catecholamine depletion. The preoperative urinary levels of norepinephrine and dopamine were abnormally high. Bilateral adrenal tumors also, confirmed postoperatively by abdominal MRI, were developing rapidly. The pathological examination revealed that the tumor was a pheochromocytoma.