A muscular band called the diaphragm separates the chest cavity from the abdominal cavity. Defects in muscles that surround body cavities are called hernias. Cats suffer from two major types: diaphragmatic hernias and peritonealpericardial diaphragmatic hernias. The former occurs as a result of trauma; the latter is a congenital defect.
When the diaphragm no longer separates the body cavities, abdominal organs move forward into the chest cavity and put pressure on the heart and lungs. Symptoms of either type of hernia include shortness of breath, difficulty breathing, rapid heart rate, heart arrhythmia, gastrointestinal upset, weight loss or general discomfort. Some cats, especially those born with the defect, show few signs. As they grow and live with the defect, they learn to compensate.