Abnormal shunt left to right atrium suggestive small atrial septal defect can this make the shunt also go right to left if so is it dangerous?

Pressure gradient: Blood will flow across a hole in the heart from the higher pressure left to the lower pressure right. If the pressure on the right increases it can become higher than the left, then flow will reverse. That is not a good thing. Most ASD are insignificant.

If RA>LA pressure: Shunt flow will direct from the higher pressure chamber to the lower pressure one. This usually results in left to right shunting across an asd. Over time, as flow into RA is increased, a corresponding increase in pulmonary blood flow will lead to pulmonary hypertension. The subsequent rise in right sided pressures will lead to reverse shunting (r to l) with cyanosis (eisenmenger).

Possibly: Any right to left shunt has the potential to be dangerous by allowing a blood clot to cross through the heart and go out to the body--and potentially cause a stroke. However, many people have asds and do not have this problem. Please provide more info or discuss your specific risks with your cardiologist.