A detailed anatomopathologic study of the various developmental malformations encountered in a set of female thoracopagus twins is presented. Special emphasis has been devoted to the analysis and description of the complex cardiovascular abnormalities associated with the conjoined heart and liver of this set of twins. The heart was conjoined with two sets of great arteries. The great arteries of one twin were d-malposed and originated from a single right ventricle; a normally placed aorta originated from a single left ventricle and the hypoplastic pulmonary trunk originated from a rudimentary outlet chamber of the other twin. One twin had two atria with the systemic veins returning to the right one and an anomalous pulmonary venous return terminating in the ductus venous of her liver. The other twin had a single right atrium plus an accessory atrial chamber to which both the pulmonary and the systemic veins returned. There were two umbilical arteries originating from the internal iliac arteries of one twin and two umbilical veins which fused into one as they entered into the ductus venous of the other twin. The cardiovascular abnormalities of our case have been compared with those encountered in 25 well-documented cases of thoracopagus twins previously reported in the literature. It was concluded that the majority of thoracopagus twins (approximately 75%) had conjoined heart with associated cardiovascular abnormalities making them unsuitable for surgical separation even at the cost of the life of one of them. In addition, an embryological interpretation concerning the possible origin of the cardiovascular abnormalities of our case is presented and discussed.