Although venous thrombosis is one of the most frequent complications of malignant disease including multiple myeloma, massive pulmonary embolism is an uncommon complication. Free-floating intracardiac thrombus has been rarely reported as a cause of acute pulmonary embolism in patients with multiple myeloma. We report a case presenting acute pulmonary embolism due to free-floating right atrial thrombus in a patient with multiple myeloma.