Hypertrophic cardiomyopathy (HCM) is a rare form of heart muscle disease. It is characterized by a thickening of the walls of the heart, which leads to an inadequate amount of blood being pumped out into the body when the heart contracts during the systolic phase. When the heart relaxes between contractions during the diastolic phase, an insufficient amount of blood will fill the chambers of the heart. Ultimately, HCM often will lead to congestive heart failure. Signs Most pets with HCM will not exhibit any symptoms of the disease. If your pet is symptomatic, it will exhibit signs of congestive heart failure. These include: • Exercise intolerance • Shortness of breath • Coughing • Bluish discoloration of the skin. Very rarely, a pet with HCM may experience a transient loss of consciousness, or fainting, during a high level of activity or exercise. During a physical veterinary examination, a pet with HCM may exhibit systolic heart murmur, and a heart gallop. Unfortunately, in most cases, the most commonly reported clinical sign of HCM is sudden, fatal heart failure.