Hypertrophic cardiomyopathy (HCM) is the most common acquired cardiac condition in catscausing thickening of the muscle within the heart. This disease processcan lead to potentially fatal consequences such ascongestive heart failure, aortic thromboembolism (blood clot dislodgement into major arteries), and sudden death due to arrhythmias. Diagnostics such as echocardiography and chest x-rays are used to monitor patients, ascertain treatment options, and determine the likelihood for the development of these potentially life-threatening conditions. Cardiac biomarkers, specific hormonal or protein-based products related to structural changes in the heart that can be detected in blood, can be used for the initial screening of patients.N-terminalpro-B typenatriuretic peptide(NTproBNP)and cardiac troponin-I(cTnI) are two specific cardiac biomarkers that have previously been shown to be significantly elevatedinHCM cats. Preliminary data on Galectin-3 (Gal-3), an indicator of fibrosis in the heart,shows promise as a biomarker in cats as it is increased in HCM catscompared to healthy cats.NTproBNP is the only cardiac biomarker that has been evaluated for biologic variability, or the normal fluctuation in this biomarker not indicatingchanges to the heart,in healthy cats. The purpose of this study is to determine the biologic variability of NTproBNP, cTnI, and Gal-3 in healthy cats and cats with HCMand the critical change value (CCV) needed to indicate a true change in disease. This information will be critical to assess the value of serially monitoring these cardiac biomarkers as a way to determine disease progression and potentially design studies using these biomarkers to assess prognosis in these patients.