Congenital atrial diverticula are rare, especially those involving the right atrium. This condition was observed in a 52 year old man who presented with palpitations. The diagnosis was made by two-dimensional echocardiography and confirmed by CT scan, magnetic resonance imaging and angiography. In the absence of significant invalidity, no treatment was recommended. Only three other cases of this condition have been previously reported, all of which were referred for surgery for thrombotic complications, arrhythmias and cardiac failure. Anatomo-pathological analysis showed different appearances: fibrous tissue and lipomatous degeneration. In the absence of associated heart disease, these aneurysms are probably congenital.