Every dog (or cat, or human for that matter) is born with a hole in his or heart. This hole works as a valve and is called the patent ductus. Its function is primarily to shunt blood to the lungs while the puppy is still in its mother's womb, and as such it becomes unnecessary after birth when the puppy can breathe on its own. Because of this, the fissure known as the patent ductus normally closes on its own by the time the animal is three days old. There are times, however, when for whatever reason, this does not occur.
In a normally functioning heart, blood enters the heart on one side and is sent to the lungs to be oxygenated, whereupon it returns to the other side of the heart where it is pumped out to the rest of the body. If the patent ductus does not close, the result is that an inordinate amount of blood is shunted towards the lungs, which causes an increase of fluid on the lungs and labored breathing. Over time, if the problem is not corrected, the left atrium of the heart will become substantially enlarged due to overworking and overflowing with fluids, and will stop working. As you can see, patent ductus arteriosis can be a very serious disease if left untreated.
Some general signs that your dog might be suffering from an unclosed patent ductus are coughing or labored breathing. In addition to this, he or she might exhibit an intolerance to exercise, or show signs of seizures or fainting during periods of high activity. A heart murmur can usually be detected as well.
A veterinarian will attempt to diagnose patent ductus arteriosis by first listening for the presence of a continuous heart murmur. Once this is confirmed, a further electrocardiogram will reveal that the left side of the heart is enlarged, thus confirming the diagnosis.
Once other potential diseases are ruled out and patent ductus arteriosis is firmly established, the treatment is usually carried out at once. In what is a fairly simple procedure as far as heart surgeries go, the open ductus is ligated and closed with sutures, thus reversing the problem instantly. If this surgery is done correctly, the animal should improve almost at once and their prognosis is usually quite good. Life span is generally not affected and the animal can return to normal levels of activity after a few weeks of rest and restricted diet. In the event, however, that this surgery is not performed, congestive heart failure is the inevitable result.
Though the prognosis for successful surgeries is good, there is a very small percentage of cases in which the fissure of the patent ductus can spontaneously reopen itself. When this happens, it's usually not sufficient to simply repeat the surgery and a much more in-depth approach will need to be taken. This secondary surgery is usually completed by a specialist and as such, it might be expensive, but the results are usually quite successful.