We report the case of a young man in whom a right paracardiac mass was resected. The histopathologic study was compatible with actinomycosis. He developed severe cardiac failure, pulmonary edema and pericardial effusion. He was treated with penicillin, during 12 months. He did well afterwards, however, the echocardiographic follow-up revealed chronic pericardial effusion and thickening and fusion of the pericardium to the epicardial wall.