Circe is feeling great after heart surgery to correct a congenital defect (PDA). She's only four months old and 3.3 pounds. As a fetus (in utero), cats, dogs, and people have a blood vessel called the ductus arteriosus that connects the aorta and the pulmonary artery, as the lungs are not filling with air and delivering oxygen to the bloodstream (they get that from maternal blood). At birth, that vessel is supposed to close. When it does not close, it is called a patent ductus arteriosus (PDA), and blood from the high-pressure aorta continues to pump through the pulmonary artery, causing progressive heart failure...most animals would die within a year or so.  
They have a heart murmur that sounds like a washing machine, and can be felt as a heavy vibration with a hand on the chest. Such a murmur is called a "palpable thrill" (I didn't invent that name, so don't ask me).
Yesterday I went into her chest and tied off the vessel. If it had torn, she would have died on the spot. The close-up image shows the silk suture surrounding the PDA.
The procedure was a success, and as soon as I tied off the vessel, the murmur stopped. Today, we pulled the chest tube, and Circe is eating and feeling like a kitten again. She should have a normal life.

Thanks to my great surgery and anesthesia team at Animal Specialty & Emergency Hospital for keeping this little kitty warm and healthy while I did the surgery.