Mutations in the tafazzin gene are the basis of Barth syndrome. The tafazzin protein is responsible for the synthesis of cardiolipin. Doxycycline-induced tafazzin-knockdown mice have been used as a model for Barth syndrome. In the current study, we examined subsarcolemmal and interfibrillar mitochondria from hearts of tafazzin-knockdown mice, focusing on mitochondrial ultrastructure, oxidative phosphorylation, electron transport chain complex activity, and phospholipid and supercomplex content. We then compared the result with mitochondrial pathology in Barth syndrome patients. Although tafazzin-knockdown mouse is a reasonable model for the study of Barth syndrome pathophysiology, it is not a precise simulacrum of the human condition.