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A comparative morphometric study of ventricular myocardial cells of the West African insect-eating bat, Pipistrellus pipistrellus the hamster and the rat revealed significant differences in volume fractions of mitochondria, myofibrils, lipid bodies and T tubules. In the cells of the bat, mitochondria constitute 35% of cytoplasmic volume compared with 29 and 30% in the hamster and rat, respectively. Notably, crista density is much higher in the bat cells (3.58 × 10⁵ cm^–1) than in those of the hamster (2.59 × 10⁵ cm^–1) and of the rat (2.48 × 10⁵ cm^–1). Myofibril concentration is 40% in the bat, 53% in the hamster and 55% in the rat. There is greater numerical density of lipid bodies in the bat (212.27 × 10⁹ cm^–3) than in the hamster (139.20 × 10⁹ cm^–3) and in the rat (114.00 × 10⁹ cm^–3). The volume occupied by T tubules is 0.02 in the bat and hamster, and 0.009 in the rat. These differences suggest structural design for efficient metabolic activity in the bat which, among mammals, has high exercise tolerance.