Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats, which can lead to congestive heart failure, sudden death, and stroke. Although current techniques allow reliable detection of heart disease, it is much more difficult to predict which cats are at the highest risk of going into heart failure or dying from their condition. In humans, it is well-established that fibrosis of the heart muscle is associated with worse outcomes and higher risks of heart failure or other adverse events. The current method for evaluating heart disease in cats largely depends on cardiac ultrasound, which is unable to assess fibrosis. Galectin-3 is a circulating protein produced by the body when fibrosis is occurring and has been found in humans to correlate to the degree of fibrosis of the heart in HCM, as well as proving useful for identifying high-risk patients. This study aims to evaluate the utility of galectin-3 in cats with HCM with a goal of improving clinician’s ability to identify cats who are at highest risk of heart failure, stroke, or death.