Cardiomyopathies are the leading cause of symptomatic feline heart disease. The incidence of occult heart disease in apparently healthy mixed-breed cats with and without auscultatory abnormalities such as murmur, arrhythmia or gallop rhythm is not well documented in the veterinary literature. Additionally, current clinical recommendations include an echocardiogram for all cats with auscultatory abnormalities. One recent study with a small sample size suggested that as many as 86% of clinically asymptomatic cats with a murmur have echocardiographic evidence of heart disease. A second report cited the presence of cardiac disease in approximately 20% of cats undergoing post mortem evaluation for sudden death. Together these findings suggest that clinically significant occult heart disease may be relatively common and represent a risk factor for an adverse clinical outcome. We propose to evaluate 100 apparently healthy mixed-breed cats of various ages to further describe the incidence of occult cardiomyopathy in cats with and without auscultatory abnormalities. Evaluation will include auscultation, indirect systolic blood pressure, thoracic radiographs, heartworm antibody, total T4, blood urea nitrogen, creatinine, packed cell volume and total solids. This study will, in addition, generate normal ranges for two dimensional echocardiographic left atrial and left ventricular dimensions and a variety of tissue Doppler parameters, as well as determine any significant correlation with a radiographic vertebral heart score. Cats with auscultatory or echocardiographic abnormalities will have annual follow-up evaluations for a total of 2 years. Data generated by this study will be entered into a new web-based feline cardiac registry.