Actinomycosis is a common chronic suppurative and granulomatous infection caused by anaerobic or microphilic bacteria primarily from the genus Actinomyces. However, Actinomyces is a rare cause of pericarditis. We experienced a rare case of pericardial actinomycosis. A previously healthy 44-year-old man presented with 3 days of fever, chest pain, and clinical signs of congestive heart failure. Chest computed tomography showed pericardial effusion, pericardial thickening, and bilateral pleural effusion. A subxiphoidpericardiotomy was performed, and a histological specimen was taken from the pericardium. A histological section of the pericardium showed an actinomycotic granule (sulfur granule). His symptoms and signs improved after administration of piperacillin/tazobactam and steroids. He was uneventfully discharged on oral amoxicillin/clavulanate. He recovered fully with no recurrence after six months of follow-up.