Abstract
We present the case of a neonatal patient with atrial tachycardia with unusual characteristics – abrupt onset and cessation, non-responsiveness to overdrive, termination by direct cardio-version – in association with an ostium secundum-type atrial septal defect and a large inter-atrial septum aneurysm. Electrocardiographic recordings showed P waves with characteristics suggesting a right low septal origin, which suggested a possible involvement of the septal aneurysm. In dealing with arrhythmias, a thorough echocardiographic evaluation is mandatory to identify underlying structural malformations and to evaluate the hemodynamic status. Further research should be made concerning mechanisms of arrhythmias in patients with an associated atrial septum aneurysm.