Heart apex rupture and haemopericardium was found to be the cause of death of three young capercaillie (Tetrao urogallus) reared in captivity. Gross and microscopic signs of myocardial fibre degeneration were present in only one bird, and circumscribed to the heart apex. The pathogenesis of the lesion is unclear, but the tachycardia due to the unusually high excitability of these birds, and predisposition for mechanical rupture in the heart apex are considered to be the more significant factors that could cause the condition. © 1991, Taylor & Francis Group, LLC. All rights reserved.