**Abstract**

Myxomatous mitral valve disease (MMVD) is the most common heart disease in dogs and has many similarities to human mitral valve prolapse (MVP). Transthoracic echocardiography is a non-invasive method for making a diagnosis and predicting the progression of heart failure (HF) in dogs and humans with mitral regurgitation (MR). It enables clinicians to detect the mitral valve (MV) lesions, to evaluate MR severity, and to assess its impact on cardiac remodeling, myocardial function, left ventricular (LV) filling pressures, as well as pulmonary arterial pressure. Furthermore, advanced ultrasound technologies such as tissue Doppler imaging (TDI), strain and strain rate imaging, and two-dimensional (2D) speckle tracking echocardiography (STE) provide a better assessment of global and regional myocardial function. Although the severity of MR and HF in dogs with MMVD is being evaluated as similar to human cardiology, the veterinary cardiologists are more focused on the severity of cardiac remodeling and cardiac dysfunction caused by MR, because surgical restoration of defected mitral apparatus is rarely done in dogs. The chapter will review conventional echocardiographic features of MMVD in dogs to provide a better understanding of the similarities and discrepancies between canine MMVD and human MVP to veterinary and human cardiologists and researchers.

**Keywords:** mitral valve prolapse, myxomatous mitral valve disease, mitral valve insufficiency, heart failure, mitral regurgitation
