And so we have the movement of blood between the two atrium of the heart. Now, normally this condition is actually not very dangerous because normally what happens is because we have a higher pressure on the left side of the heart, then on the right side of the heart, a tiny bit of that oxygenated blood inside the left atrium will go into the right atrium. And so we have some of that oxygenated blood reaching the right atrium, and it will basically return back to the lungs via the pulmonary trunk. Now, however, even though we have a tiny bit of blood going into the right atrium, there is still enough blood inside the left atrium to actually go into the left ventricle and eventually pump to the tissues and organs and systems of the body. So normally, this is not a big problem. However, what it can cause is an embolism.