What is pigeon heart condition?

Pigeon heart syndrome—an abnormality resulting from chronic high blood pressure that causes the left side of the heart to become enlarged—does not affect humans but, rather, horses (as well as certain dogs). Its name, as well as that of another heart condition seen predominantly in horses—aortic stenosis—were coined by equine pathologists and radiologists because these cardiac conditions cause changes in cardiac shape resulting in an appearance not too dissimilar to the hearts of birds.