If there is right to left shunting, there is a greater risk of stroke as the blood from the right atrium has not been filtered through the lungs. If the shunting is left to right, the oxygenated blood will pass on to the lungs without a problem...a problem, if any, is less oxygenated/blood going into circulation with each heartbeat.
There is bi-directional shunting indicating there is left to right and right to left shunting depending intra chamber pressure.