Subacute and chronic mountain sickness of humans and the related brisket disease of cattle are characterized by right-sided congestive heart failure in individuals living at high altitudes as a result of sustained hypoxic pulmonary hypertension. Adaptations to high altitude and disease resistance vary among species, breeds, and individuals. The authors conducted a retrospective survey of right-sided cardiac hypertrophy associated with pulmonary arterial hypertrophy or arteriosclerosis in zoo mammals housed at Africam Safari (Puebla, México), which is located at 2,100 m above sea level. Seventeen animals with detailed pathology records matched the study criterion. Included were 10 maras (Dolichotis patagonum), 2 cotton-top tamarins (Saguinus oedipus oedipus), 2 capybaras (Hydrochaeris hydrochaeris), and 1 case each of Bennet's wallaby (Macropus rufogriseus), nilgai antelope (Boselaphus tragocamelus), and scimitar-horned oryx (Oryx dammah). All had right-sided cardiac hypertrophy and a variety of arterial lesions restricted to the pulmonary circulation and causing arterial thickening with narrowing of the arterial lumen. Arterial lesions most often consisted of medial hypertrophy or hyperplasia of small and medium-sized pulmonary arteries. All maras also had single or multiple elevated plaques in the pulmonary arterial trunk consisting of fibrosis, accompanied by chondroid metaplasia in some cases. Both antelopes were juvenile and died with right-sided congestive heart failure associated with severe pulmonary arterial lesions. To the authors' knowledge, this is the first description of cardiac and pulmonary arterial disease in zoo mammals housed at high altitudes.