Gus has two congenital defects. The first is a VSD which is fairly common and is a hole between the left and right halves of the heart. His defect is small and by itself was not likely to become an issue for him. The second defect is a double chambered right ventricle. This means he has a fibrous membrane dividing this chamber of the heart in two. This causes the pressure to increase in this half chamber, which causes the heart to work harder, which causes the wall to thicken, which further increases the pressure in a vicious cycle. This increase in pressure also pushes the blood through the VSD and into the opposite side of the heart before it has had a chance to circulate through the lungs and become oxygenated. This non oxygenated blood is then circulated back through the body causing his symptoms.
There is a (very expensive) surgery that can correct this by inserting a specialized balloon that breaks down the membrane. This surgery has the potential to give him a normal life. Although significant complications directly related to surgery are rare there is the risk that the membrane won't be broken down enough to improve his clinical condition and that the membrane may grow back. Because the condition is so rare there are no meaningful statistics on the likelihood of this. However, without surgery he will not have a normal quality or length of life. At this time the rescue has decided to pursue surgery and give Gus a chance at a better life.
He’s looking sad in this picture because he peed in the house. I’ll be glad when he’s healthy enough to neuter. We probably could now, but have elected not to take the risk.