What may be happeining is a left to right shunting of oxygenated blood. The shunt is due to a hole between the two upper chambers, and some of the oxygenated blood goes into the right upper chamber and is pumped back to the lungs rather than going into the system. The increase of blood in the right atrium can cause pulmonary hypertension and increase the size of right atrium.
If there is moderate to severe shunting permitting a large amount of blood to pass through to the right side of the heart, the right atrium, right ventricle, and lungs will become overworked, and symptoms may be noted: fatigue, sweating, rapid breathing,
shortness of breath.
It iws difficult to put a time factor to progression if any without more information, information your doctor should have to consider and make a decision..