Primary cardiac lymphoma (PCL) is one of the rarest tumors of the heart. The most common type is diffuse, large B-cell lymphoma. Most often, the right atrium and the right ventricle are involved, and if not diagnosed and treated in time, it can be fatal. In this case, a female patient underwent an urgent operation for a large, infiltrative, right atrial mass. Extensive resection of the lateral walls of both atria and the interatrial septum as well as reconstruction were performed successfully. The pathological evaluation suggested PCL. The aim of this case is to raise awareness of this disease and to highlight clinical and surgical approaches.