A 24 year old female with no significant past medical history presents to her primary care physician with exercise intolerance. She has been trying to exercise to lose weight but becomes short of breath after only minimal effort. Her temperature is 37.0, blood pressure 110/70, heart rate 110, respirations 20, and oxygen saturation 94% on room air. Physical examination reveals normal jugular venous pressure, normal breath sounds, a II/VI systolic murmur at the left upper sternal border and a fixed split S2 heart sound. Laboratory studies are normal. ECG reveals normal sinus rhythm, a right bundle branch block, and left axis deviation. Which of the following is her likely diagnosis?
A. Ostium primum atrial setpal defect
B. Ostium secundum atrial septal defect
C. Ventricular septal defect
D. Patent ductus arteriosis
E. Ebstein's anomaly