By far, the most likely etiology for left-sided congestive heart failure in a mature cat is HCM. Other types of cardiomyopathy, such as restrictive, unclassified, or dilated, are possible but are more rare. For more information on other feline cardiomyopathies, go the following link. Congenital diseases may also need to be considered in young cats. A cardiac ultrasound exam is necessary for definitive diagnosis. Dante’s echocardiogram showed moderate left ventricular hypertrophy and left atrial enlargement, and evidence of dynamic left ventricular outflow obstruction, thus further characterizing the HCM as the obstructive type. Dante’s episode of collapse may be attributed to left ventricular outflow obstruction or to a tachyarrhythmia, as evidence of both were found in this case.