At one end of the severity spectrum, early chronic valvular disease, some forms of hypertrophic cardiomyopathy and some mild congenital heart defects may have little effect on an animal's lifestyle or life expectancy; at the other end, severe heart failure can interfere with even simple activities and prove rapidly fatal. (cvm.ncsu.edu)
In chronic valvular disease the heart valves do not close in the right way, causing problems with the way blood flows through the heart and leaks. (dog-health-guide.org)
Toy dogs and small breeds usually develop heart failure as a result of chronic valvular disease that is accompanied by regurgitation of blood through the mitral and / or tricuspid heart valves. (petwave.com)