The aim of this study was to evaluate systolic function of left ventricle in dogs with spontaneous mitral regurgitation by estimating the rate of pressure rise in the left ventricle (dP/dt). Ninety-three dogs of different breed and sex, with chronic degenerative valvular disease were examined. All dogs had echocardiography examination with dP/dt estimation assessed from mitral regurgitant jet using continuous Doppler-echocardiography. The dogs were divided into four classes of heart failure according to NYHA class. Results: dogs in NYHA I dP/dt = 2,142 ±1,309, SF=33.6±10.5, EF=66.58± 14; NYHA II dP/dt = 3,062 ±1,798, SF=42 ±10, EF=76.5 ±11.5; NYHA III dP/dt = 3,483 ±2,136, SF=44.2 ±21, EF=75.7 ±13; NYHA IV dP/dt = 4,496 ±1,797, SF=40.6 ±6, EF=70.4 ±16. Dogs with chronic cardiac insufficiency and mitral insufficiency due to chronic degenerative valvular disease had no echocardiograhic evidence of left ventricular systolic dysfunction assessed from mitral regurgitant jet dP/dt.