What is a PDA in the Heart of a Cat or Kitten? A PDA is referring to a Patent Ductus Arteriosus of the heart.
Per the Cornell Feline Health Center:
Congenital heart defects are fairly rare in cats (estimated to be around one to two percent of new born kittens) but patent ductus arteriosus (PDA) is one of the more commonly reported defects. During the time that a kitten is developing in its mother's womb, the ductus arteriosus connects the pulmonary trunk (the major blood vessel leading from the heart to the lungs) and the aorta (the major blood vessel leading from the heart to the rest of the body) to allow oxygen-rich blood to bypass the fetus' non-functioning lungs. Normally, the ductus arteriosus closes down within several days after birth, but if it stays open (patent), blood continues to bypass the lungs to a certain extent and eventually causes congestive heart failure.
Most cases of PDA are detected during the kitten's first veterinary examination. A fairly characteristic type of heart murmur is usually present, but to confirm the diagnosis and to make sure that there are no other heart defects, an ultrasound examination of the heart (echocardiography) is highly recommended. The preferred treatment is surgical closure of the patent vessel. If surgery is performed early enough, a normal lifespan can be expected, but if it is delayed, irreversible changes take place that will ultimately shorten the life of the kitty. Without surgery, the prognosis is poor; death due to congestive heart failure generally occurs anywhere from one month to five years of age.