We describe the findings in a six-year-old girl who presented with signs of left atrioventricular valvar insufficiency. The echocardiogram showed a common atrioventricular junction, intact atrial and ventricular septal structures. At surgery, the left-sided atrioventricular valve was found to be tri-foliate, and corrected by valvoplasty. To the best of our knowledge, this is the first case of atrioventricular septal defect with common atrioventricular junction and intact septal structures diagnosed during life.