The circulatory system delivers vital oxygen to the tissues in the body and carries wastes from the tissues to be excreted. The cycle of blood circulation begins in the heart. The heart pumps blood through the lungs to fill up with oxygen. From the lungs, oxygen-rich blood returns to the heart to be pumped out to the tissues. After delivery of oxygen the tissues, blood collects wastes (e.g.: carbon dioxide) from the tissues. Oxygen depleted blood, containing wastes, returns to the heart once again to be pumped to the lungs to rid itself of carbon dioxide while simultaneously acquiring more oxygen.

If your horse experiences heart problems, you may notice: coughing, poor performance/exercise intolerance, pale gum color, cold extremities, weakness, lethargy, collapse, poor appetite, and/or labored breathing. Some heart abnormalities may be found incidentally by your veterinarian-your horse may have no outward signs of a problem.

Common abnormalities of the heart and circulatory system include:

  • Inability to effectively pump blood through the body as is seen with heart failure.
  • Electrical disturbances within the heart. The heart possesses an entire electrical system to activate the heart muscle to pump blood. If there is a block in this circuit or an abnormal circuit develops, the heart cannot pump effectively. Examples include: Atrial Fibrillation and Ventricular Tachycardia.
  • Incorrect plumbing pathways through the heart cause pumped blood to travel in uncoordinated directions. Some heart and blood vessel malformations develop before birth (e.g.: Ventricular Septal Defect, Tetrology of Fallot), while others develop as your horse ages (e.g.: Tricuspid Valve Insufficiency; Mitral Valve Insufficiency; Aortic Regurgitation).
  • Heart muscle abnormalities caused by Myocarditis (e.g.: Dilated Cardiomyopathy)
  • Vasculitis : Inflammation of the blood vessels
  • Thrombosis, Thrombophlebitis : inflammation within a vein promotes clots to form. These clots lodge within the blood vessel resulting in complete or partial obstruction of normal blood flow.

Blood, although a liquid, is a tissue: it is filled with cells. Blood carries red blood cells to deliver oxygen and white blood cells to ward off infection. The water portion of blood surrounding the cells contains nutrients, proteins, and hormones that are essential for life. Your horse may experience deficiencies and/or excesses of any of these blood components, leading to disease.


What makes your horse’s heart tick? A horse’s four-chambered heart is a complex, synchronized network of electrical circuits that weaves through the cardiac muscle. The heart is the pump at the center of the circulatory system. This system delivers vital oxygen to the tissues in the body and carries wastes from the tissues back to the lungs to be exhaled. Problems within the circulatory system may involve abnormal: 1)blood flow (heard as a murmur), as in congenital defects and valve leakage; 2) heart muscle function, termed cardiomyopathies; and 3) electrical signals in the heart muscle (e.g.: ventricular tachycardia), causing uncoordinated contractions of the heart. Indications that your horse may have a heart problem include: poor athletic performance, cold extremities, weakness, collapse, and/or changes in breathing patterns.

What's Next

  • 1

    Call us to schedule an appointment

  • 2

    Meet with a doctor for an initial exam.

  • 3

    Put a plan together for your pet.