Hypertrophic cardiomyopathy (HCM) is characterised by left ventricular thickening in the absence of abnormal loading conditions. Although, ‘true’ HCM (familial/genetic) is an exclusion diagnosis, as several conditions cause increased left ventricular thickness mimicking HCM. These are sometimes called HCM phenocopies (HCM mimickers). Besides HCM, in cats an increased left ventricular wall thickness has been described in individuals with abnormal loading conditions (hypertension, aortic stenosis); endocrine disorders (e.g. hyperthyroidism, acromegaly); dehydration (pseudohypertrophy), transient myocardial thickening and infiltrative disease (cardiac lymphoma). It is paramount for any clinician to recognise the most common causes of HCM phenotype, as these may have different therapies and prognosis and thus influence both the clinician and owners’ decisions. In this lecture, we will review the HCM phenocopies that have been described in cats thus far and discuss some controversies on HCM phenotypes and phenocopies in cats.