Although most feline heart disorders are diagnosed in middle-aged and elderly cats, some kittens are born with them. Fortunately, these congenital cardiac conditions are relatively rare, occurring in only one or two percent of kittens. The most commonly diagnosed among these disorders are: ventricular septal defect (VSD), patent ductus arteriosus (PDA), and mitral valve dysplasia (MVD).

Understanding the nature of these conditions requires a basic awareness of the feline heart’s structure and function. About the size of a small apricot, it is a 4 chambered, muscular organ located in the center of the chest. Its main function is to pump blood, thereby (1) ridding the circulating blood of waste products (mainly carbon dioxide and nitrogen containing compounds), and (2) providing the body with a steady supply of oxygen-rich circulating blood. Both the left and right sides of the heart have an upper chamber (atrium), which collects blood, and a muscular lower chamber (ventricle), which pumps blood. First, the right atrium collects oxygen-depleted blood from the body, and when the chamber is full, propels it into the right ventricle. From there it is pumped, via the pulmonary artery, into the lungs, where the carbon dioxide is removed and its oxygen supply is replenished. The blood then moves from the lungs to the left atrium and subsequently to the left ventricle, from which it is pumped, via the aorta, into the body’s circulatory system. In a healthy cat, the four heart chambers are separated internally by muscular walls (septa) and by one-way valves that keep blood moving in the proper direction. The most frequently diagnosed congenital disorders involve problems associated either with the heart’s valve structure and operation or with holes in the septa.

Most common of all is ventricular septal defect (VSD), which is a hole in the ventricular septum, the muscular tissue that separates the left and right ventricles and prevents blood from being diverted (shunted) from one of these lower chambers to the other. The size of the hole and the pressures on each side of the septum determine the direction and amount of blood flow that shunts across a VSD.  A small VSD is commonly of no significance, and an affected kitten can be expected to thrive and live a normal life. A moderate or larger hole, though, may cause enough shunting of blood to produce clinical signs, such as open-mouth breathing and exercise intolerance. If the hole is large enough, the cat can develop congestive heart failure.

The second most common congenital cardiac condition is patent ductus arteriosus (PDA). Prior to birth, a blood vessel called the ductus arteriosus connects a fetus’s aorta to its pulmonary artery, which leads to the lungs. In a normal kitten, this vessel closes within a day or two of birth. But in the case of a PDA, the ductus arteriosus remains open (patent), resulting in excessive passage of blood from the animal’s heart to its lungs. Although the condition can potentially lead to heart failure, it can be surgically corrected (either tied off or closed using a clip) within a few months after a kitten is born, or even earlier if the surgeon thinks the kitten is big enough and healthy enough.

Another commonly diagnosed congenital cardiac disorder in cats is mitral valve dysplasia (MVD). In this condition, the mitral valve, which normally keeps blood flowing in one direction from the left atrium to the left ventricle, is malformed and becomes leaky, allowing blood to flow backwards into the left atrium when the ventricle contracts. This can lead to the development of congestive heart failure resulting in clinical signs of difficulty breathing, exercise intolerance, weight loss, and/or vomiting.  Cats with dilated atria may also develop blood clots that may be ejected into their arteries, a devastating process that may block blood supply to organs and/or muscles and cause significant clinical problems.

Less commonly encountered congenital heart defects in the cat include stenosis (or narrowing) of the pulmonic valve, which separates the right ventricle from the pulmonary artery, or of the aortic valve, which separates the left ventricle form the aorta.

A common feature of congenital heart defects is the presence of a heart murmur.  A heart murmur is an abnormal, usually whooshing and/or harsh sound that can be heard using a stethoscope during a physical examination. Heart murmurs are caused by turbulent blood flow that is induced by these defects. Echocardiography is generally the best means of diagnosing congenital heart defects.

Although some kittens with congenital heart defects may respond favorably to medicinal or, in some cases, surgical treatment, the prognosis for severe and /or multiple congenital cardiac defects is often, unfortunately, poor. Minor defects, however, may be well tolerated and may even be associated with a normal lifespan.

Last updated 2021