Comparative morphologic, morphometric and histological studies was carried out on adult male hearts of the three mamalian species namely the Rabbit (Oryctolagus cuniculus),Wistar rats (Rattus norvegicus) and African giant rats (Cricetomys gambianus). Five animals from each species were weighed, lightly anasthetized with chloroform and huma- nely sarcrificed. The thoracic cage was carefully opened and the hearts were removed, morphologically observed andfixed in Bouins fluid. The tissues were processed for histological studies and stained using Haematoxylin and eosin (H &E) and Rafferty's stain. The hearts were physically observed to be reddish in colour and pear shaped. The heart of the three mamalian species showed the aorta, superior and inferior vena cava and the pulmunary vessels similar to that of the humans. The mean total body weight of the African gaint rats, Rabbits and Wistar rats are 1.167±0.153 kg, 1.233±0.252 kg and 20.333±5.774 g respectively, which showed a significantdifference (P≤ 0.01) between the body weight of the African gaint rats, Rabbits and the Wistar rats. The mean weight of the hearts of African giant rats, Rabbits and Wistar rats are 4.367±1.620, 3.306±0.115, 0.766±0.164 gms respectively which showed asignificant difference (P≤0.01) between the hearts of African gaint rats, Rabbits and Wistar rat. Histologically, the atrial and ventricular parts of the heart of the three species showed great similarities in terms of the arrangement of the cardiac muscle cells and the layersof the walls of the heart in the three mamalian species with little differences observed in the morphometrics of the muscle fibres and intramuscular cellular distributions in the different hearts studied which could be due to the sizes of the mammals in general.