A 78-year-old man diagnosed with single atrium as congenital heart disease.

Single atrium is a rare congenital heart disease characterized by complete absence of the interatrial septum. It occurs as an isolated cardiac defect, or as a part of skeletal, muscular, ophthalmologic, and vascular malformations to signify congenital syndromes. A 78-year-old male patient presented with generalized body swelling of 2 weeks duration. He had associated shortness of breath, orthopnea, productive cough, and palpitation. Upon physical examination, blood pressure = 150/75 mmHg, pulse rate = 50 bpm, respiratory rate = 24 bpm, and T ° = 36.7 °C. He had signs of pleural effusion on left lung field. Cardiovascular examination revealed mean heart rate of 50 beats/min with irregularly irregular pulse rhythm, raised jugular venous pressure, and pansystolic murmur at left lower sternal border. He had tender hepatomegaly, ascites, and pitting leg edema. Chest X-ray showed cardiomegaly, prominent pulmonary trunks, and left-sided pleural effusion. Electrocardiography revealed atrial fibrillation, bifascicular block (right bundle branch block and left anterior fascicular block) with mean heart rate of 50 beats/min. Two-dimensional transthoracic echocardiography showed complete absence of interatrial septum (single atrium) without atrioventricular defect and interventricular communication. Diagnosis of heart failure secondary to congenital heart disease (single atrium) with atrial fibrillation and bifascicular block was made based on clinical and imaging evaluation. Well-tolerated symptoms of a single atrium until late adulthood could be explained by the presence of streaming or incomplete mixing of blood within the atrium, in which the more oxygenated blood is directed to the systemic circuit.