11: Cardiovascular Health

Action Point: Be aware of the signs that may indicate cardiovascular problems in the horse.

Rationale: Heart problems are not common in horses, however, they are not immune to them. If any of the following changes are observed in a horse, it may be an indication of a cardiovascular problem.

• Loss of condition
• Increased fatigue during exertion
• Shortness of breath
• Increased rate or effort of breathing
• Weakness occasionally resulting in collapse or fainting
• Signs of fluid accumulation in the abdomen or beneath the skin of the lower thorax

Heart murmurs are generally the most common, and in most cases benign of the cardiac disorders that can afflict horses. The majority of heart murmurs are physiologic, or normal, and can occur in conjunction with an excited state or a bout of colic. More serious cases could be caused by turbulence or increased velocity of blood flow due to a leaky heart valve. A specialist will be able to determine whether a heart murmur is considered incidental or merits further examination.

Horses can also be affected by congenital heart defects that are present at birth. Though these are much rarer in horses compared to humans and dogs. The first sign of a congenital heart defect is usually a murmur heard within the first few weeks or months after birth. These include ventricular septal defect (a hole in the heart) and patent ductus arteriosus (which will resolve on its own in most cases) – again, congenital heart defects are very rare in horses. 

Degenerative or acquired heart disease, such as arrhythmias, atrial fibrillation, and valvular heart disease may occur in horses older than 5 years of age, and very rarely in younger horses. Although still relatively uncommon, acquired heart disease has a slightly higher frequency of occurrence relative to congenital heart defects.

Myocardial disease is toxic damage to the heart muscle following an infectious disease like strangles, influenza or an internal abscess, and in rare cases a severe dietary deficiency of vitamin E or selenium, or the ingestion of a toxic chemical found in cattle feed.

Thrombophlebitis, a firm clot in a small part of the jugular is the only vascular condition that affects horses. It is usually the result of repeated trauma to the jugular from repeated puncture of the vein, injections or use of a jugular vein catheter.

Aorto-iliac thrombosis is a condition that affects the hind limbs, resulting in signs of lameness, stiffness, weakness and abnormal gait. The result of a clot that forms where the abdominal aorta branches toward the hind legs, this condition is progressive and rarely reversible.

The Equine Power Plant Unequaled!

*refer to summary of article in Functional Anatomy - Week 5: Activities