A medium fixed defect of the anteroseptal wall means that there is an area of the heart that does not contribute to the heart's pumping function.
This could explain the decreased ejection fraction EF (normal range is 55-70%).
The wall dividing the left and right sides of heart is called anteroseptal wall and is fed by the Left Anterior Descending (LAD) coronary artery.
This defect can be caused by i.e. a prior heart attack from a vessel blockage.
There may not be any treatment available.
Did your doctor not explain the echo results?