Humans don't have a monopoly on heart disease - our furry friends also are susceptible to a wide range of cardiovascular conditions. Smaller breed dogs, in particular, are more likely to develop heart disease, including heart "murmurs."
Heart murmurs occur when the animal's heart function has deteriorated, creating an abnormal blood flow within the heart's chambers. The condition may be congenital, meaning the animal was born with the problem, or else it can develop as the result of disease and aging. Some conditions aren't very serious; others will progress rapidly, causing congestive heart failure and death. [...]
In dogs, heart failure is usually characterized by problems with the mitral valve. This is especially true of smaller breeds, but is applicable to at least some extent with all dogs. The mitral valve refers to the muscular valve that separates the left atrium and ventricle. Its function, when working properly, is to prevent the back flow of blood once it has passed through one section of the heart to increase the efficiency of the heart's pumping, i.e. - each portion of blood that passes through the heart only needs to be pumped once because the mitral valve prevents it from flowing backwards. Over time, however, this valve begins to shrink and harden as a natural consequence of aging. [...]
One of the myriad heart problems which can affect your pet is a condition known as aortic stenosis or subvalvular aortic stenosis. With this condition, the blood flow is partially blocked as it leaves the left side of the heart (the left ventricle) into the aorta, which is the major blood vessel that transports blood to the rest of the dog's body. The obstruction can be a small nodule or a fibrous band of tissue, either of which is usually located just below the aortic valve, which is the dividing structure between the heart and the aorta.
Because of this obstruction, the dog's heart must work harder to pump an adequate supply of blood to the dog's body. Over time, this valve usually narrows even further, a condition known as stenosis. [...]
Every dog (or cat, or human for that matter) is born with a hole in his or heart. This hole works as a valve and is called the patent ductus. Its function is primarily to shunt blood to the lungs while the puppy is still in its mother's womb, and as such it becomes unnecessary after birth when the puppy can breathe on its own. Because of this, the fissure known as the patent ductus normally closes on its own by the time the animal is three days old. There are times, however, when for whatever reason, this does not occur.
In a normally functioning heart, blood enters the heart on one side and is sent to the lungs to be oxygenated, whereupon it returns to the other side of the heart where it is pumped out to the rest of the body. If the patent ductus does not close, the result is that an inordinate amount of blood is shunted towards the lungs, which causes an increase of fluid on the lungs and labored breathing. [...]
A heart murmur can be determined as a swishing sound heard by the veterinarian when examining a cat. The murmur occurs because of a heart valve malfunctioning. A heart murmur isn't a disease in and of itself but does point to heart and other medical problems.
[-]A heart valve can be too thick or damaged and as a result it doesn't close properly. When this happens blood will escape from the valve and spill into the surrounding areas. The swishing sound confirms that there is some kind of leakage going on at the time the value is closing (contracting). There are different classifications of heart murmurs depending on the turbulence (unsteady flow) and velocity, (speed of the blood flow).[/-]
[-]The classification simple heart murmur is due to value malfunctioning. The classification functional heart murmur is due to valve problems and extracardial (outside the heart) factors, which could be other medical conditions.[/-] [...]