Common ventricle with separate pulmonary outflow chamber in a horse.

The research investigates a unique case of a horse having a three-chambered heart and experiencing poor growth rate and exercise intolerance. This situation was made evident post-euthanasia, clearing suspicions of the animal having ventricular septal defect or a variant of tetralogy of Fallot.

Case Background

• The subject of study was a 3-year-old filly dealing with poor growth rate and consequent exercise intolerance.
• Initial suspicion, based on clinical and laboratory examinations, indicated the horse could either be suffering from ventricular septal defect or a variant of tetralogy of Fallot, both of which are heart-related abnormalities.

Findings

• The filly was euthanized for the purpose of the investigation.
• Postmortem findings revealed that the horse had a unique three-chambered heart condition known as cor triloculare biatriatum.
• Normally, a horse’s heart has four chambers—two atria and two ventricles. But this filly had two properly formed atria and one large common ventricle where the right and left atrioventricular orifices opened.
• The aorta, the main and largest artery in the body carrying oxygenated blood from the heart to the rest of the body, arose from this common ventricle.

Unique Heart Structure

• There was a small separate chamber where the pulmonary trunk originated. The pulmonary trunk is a major vessel that arises from the heart to supply blood to the lungs.
• This separate chamber was found to communicate with the common ventricle through a large oval opening situated along the dorsal border of the displaced interventricular septum – which is the stout wall dividing the ventricles of the heart.

These observations contributed to the understanding of heart anomalies in horses which can cause growth issues and exercise intolerance. This knowledge can further assist veterinarians in detecting and possibly treating these conditions in the future.