Cor triatriatum is a rare congenital defect that one of the atrial chambers especially left atrium, is divided into two by a fibromuscular membranee. Ankylosing spondylitis is a chronic systemic inflammatory rheumatic disorder that cardiovascular involvement can be seen. 27-year-old woman, who has been followed for ankylosings pondylitis searched for cardiac involvement, Cor triatriatum was diagnosed with echocardiography and diagnosis was confirmed with MRI and CT angiography. Membrane was resected surgically under cardiopulmonary bypass with cardioplegic arrest. Patient was discharged from the hospital with recovery. In conclusion, patient with ankylosing spondylitis must be searched for cardiac involvement.