A successfully treated case of one-year-old girl of common atrium associated with bilateral superior vena cava and an interrupted inferior vena cava with hemiazygos continuation is reported. In addition to these anomalies of systemic venous connection, both atrial appendages show morphological characteristics of left type, and the final diagnosis of left atrial isomerism was made. In the corrective surgery, atrial septation was reconstructed using trimmed autogenous pericardial patch to allow the left superior vena cava to drain into the right side of the common atrium. The patient had been pointed out bradycardia (50-100/min) since her birth. Postoperative electrocardiogram also showed bradycardia (78-100/min). Especially in sleeping, her heart rate was 50-60/min, resulting in A-V junctional escaped rhythm and A-V dissociation. This fact suggests that her sinus node is absent or hypoplastic, one of the characteristics of left atrial isomerism. Since left atrial isomerism is reported to cause a decrease of atrial rhythm with aging, careful postoperative observation on specific arrhythmia is necessary.