Caval syndrome is also known as liver failure syndrome. It is a serious complication of chronic heartworm disease in pets. Pets with caval syndrome cannot be treated like other pets with heartworms.


Caval Syndrome is caused when the number of adult heartworms is high and for lack of additional space in the main pulmonary artery some of the heartworms move to the vena cava causing signs and symptoms much different from the typical pet with heartworms.

The vena cava is the vessel that delivers venous blood from the lower half of the body to the right atrium of the heart.  When heartworms cause obstruction of this vessel, life threatening consequences ensue.  The blood undergoes hemolysis as it passes by the heartworms in the vena cava.  This causes the pet to become jaundice (yellow color to the tissues) and also will cause hematuria (blood in the urine).  In more acute cases collapse is seen with the pet presenting in lateral recumbency.

Animals with caval syndrome are usually moderately anemic from the hemolysis and have an elevation of liver enzymes from the passive congestion of the liver.  This passive congestion is caused by severe obstruction of blood flow from the lower part of the body into the heart.

Caval syndrome is also called “liver failure syndrome”.  There is a characteristic heart murmur that accompanies caval syndrome that has a third heart beat which results in an irregular gallop.  Mild cases of gallop rhythm will have very few symptoms – perhaps only a jugular pulse or mild elevation of the bilirubin and liver enzymes.

Ultrasound evaluation of these pets will show heartworms interfering with the action of the tricuspid valve.  Pets with caval syndrome cannot be treated like other pets with heartworms.  Heartworm extraction must be done prior to the more traditional therapy.  This is done as an emergency procedure in the acute cases with light sedation and local anesthesia and under general anesthesia in the mild cases.  The procedure involves passing extraction forceps or a wire with brush bristles down the jugular vein into the vena cava as shown in the following illustration.

The forceps are used to grab heartworms and pull them out of the heart.  This can be done under ultrasound guidance.  Dr. Garner has done this procedure successfully many times and there are two videos demonstrating this technique.