Diffuse large B cell lymphoma, light micrograph. Primary cardiac lymphomas are rare. They represent 1% to 2% of all primary cardiac tumours and 0.5% of all lymphomas. They are more common in immunocompromised individuals. The right atrium and right ventricle are more often involved. More than 80% of cases are non-Hodgkin lymphomas of diffuse large B-cell type (shown here). They are composed predominantly of large cells with the morphology of centroblasts or immunoblast.