The diaphragm is a muscular partition that separates the abdomen and the chest.  A tear in this thin muscle is called a diaphragmatic hernia or rupture.

The most common cause of diaphragmatic hernia is blunt trauma, such as being hit by a car or falling from a high place.  A congenital diaphragmatic hernia that results from defective development of the fetus is seen in puppies or kittens.

Once the diaphragm is torn, abdominal contents are able to enter the chest cavity.  This compresses the lungs and prevents them from fully inflating, causing respiratory distress.  The abdominal contents can also press against the heart and cause abnormal heart rhythms.  Fluid can leak into the chest cavity, further worsening heart and lung function.

Signs depend on the size of the tear and the amount of abdominal contents that move up into the chest cavity.  With small tears and most congenital hernias, there may be no obvious signs.  However, in most cases, the pet may have some breathing difficulties, especially during stress or exercise, and mild gastrointestinal upset.  In severe cases, the pet may have much more trouble breathing and abnormal heart rhythms.

Diagnosis is based on history, physical examination, and x-rays.  Sometimes, ultrasound or special x-ray dye studies are needed.

Treatment requires surgical repair. In cases of recent trauma, the pet must be stabilized before the hernia can be corrected.  Prognosis after surgery is initially guarded because of the seriousness of the operation and the risk of complications.

Congenital hernias in females are often discovered and repaired when the pet is spayed.