The Normal Heart

Located approximately in the center of the chest cavity, the heart is a hollow organ that serves as a double pump.  The heart wall is made up of a special type of muscle called myocardium.  The function of the heart is to pump blood through the circulatory system to all other body tissues.  The heart is separated into two separate pumps, the "right heart" and the "left heart".  Each side of the heart is made up of two hollow chambers: the upper chamber is the atrium, it receives the blood; the lower chamber is the ventricle, it pumps blood from the heart.  The atria and the ventricles communicate with each other, but blood does not flow directly from the right to the left side.  Thus the right and left atria and the right and left ventricles are distinct.

Blood flow is unidirectional and is directed by a series of valves.  Contraction of the myocardium drives blood flow and the valves prevent blood from flowing in the opposite direction.

A droplet of blood inside the right atrium flows passively into the right ventricle when the myocardium relaxes.  Contraction of the myocardium propels the drop of blood from the right ventricle into the pulmonary artery and the lungs.  Within the lungs, the drop of blood gives up carbon dioxide and picks up oxygen.  From the lungs, the oxygen rich blood flows through the pulmonary veins into the left atrium.  Again, when the myocardium relaxes, the blood drop flows passively from the left atrium into the left ventricle.  The next heart beat, or myocardial contraction, propels the drop of blood from the left ventricle into the aorta and into systemic circulation, where it will oxygenate and nourish the body's tissues.

Heart Disease

Heart disease is one of the more common problems encountered in veterinary medicine.  Heart disease can be divided into two broad categories: heart valve disease and heart muscle (myocardial) disease.  In both cases, the heart must work much harder to pump the same amount of blood and heart function is compromised.  The heart and circulatory system have built in mechanisms for compensating for heart disease but eventually, the heart fails and blood flow is inadequate.  

Heart disease is diagnosed based upon clinical signs, physical exam and specialized tests.  Cough, especially at night and in the morning upon awakening, is the hallmark sign of heart failure.  Exercise intolerance, abdominal enlargement, anorexia and weight loss, respiratory distress and pale gums are also common complaints.  Patients with heart failure due to valve disease often have heart murmurs.  Patients with heart muscle disease often have distinctive arrhythmias.  X-rays are used to help diagnose heart disease since one of the hearts compensatory mechanisms is to grow in size and become "stronger".  Electrocardiograms or EKG's, are used to evaluate the electrical activity of the heart and are often useful in diagnosis of heart disease.  Definitive diagnosis of heart disease requires an echocardiogram.  Echocardiogram uses ultrasound to image the heart and document specific abnormalities.

Heart disease can be controlled via the use of oxygen therapy, diet reconstruction, oral medications and exercise restriction.  Dogs and cats with heart disease also require check-ups to monitor progression of disease.  How well your pet does at home will depend upon how advanced the disease is and how well you are able to carry out your veterinarian's instructions.  By adhering to the professional advice of your veterinarian and with your own careful attention, your pet will be able to live a more comfortable and longer life.