Primary cardiac lymphoma (PCL) is a rare tumor for which no treatment strategy has yet been established. This report presents the case of a large PCL that was successfully treated by emergency surgical resection combined with postoperative chemotherapy. A 60-year-old male was referred because of dyspnea on effort. Echocardiography and computed tomography scans revealed a 10 cm tumor in the right ventricle and right atrium. The tumor was suspected to be malignant because positron emission tomography/computed tomography showed a high uptake at the tumor site. The tumor was large enough to cause life-threatening obstruction, and cardiologists were therefore reluctant to perform a percutaneous biopsy. The patient underwent emergency resection. The postoperative course was satisfactory, and the diagnosis of diffuse large B cell lymphoma (DLBCL) was thus confirmed. The patient achieved complete remission after being treated with chemotherapy for DLBCL. He was alive 1 year after surgery, without any signs of recurrence.