Previous studies have shown there to be considerable inter-specific variation in the cardiovascular anatomy of five of the six families of caecilians. Observations on the previously unstudied Rhinatrematidae reveal this family to be characterized by a number of cardiovascular features that are unique within the Gymnophiona. These include a poorly developed sinus venosus sinistra, a short truncus arteriosus, separate carotid and systemic arches and the right atrium larger than the left. Character analysis indicates that these unique features are primitive within the Gymnophiona and they provide considerable additional support for the hypothesis that the Rhinatrematidae are the sister-group to all other caecilians. This hypothesis appears to be among the best supported hypotheses of relationships within the Gymnophiona. Caecilian cardiovascular variation provides a useful source of evidence for phylogeny reconstruction that should be integrated into phylogenetic studies of the group.