A circulatory system become compulsory for the transport of nutrients and gases due to the growth of animals and the development of various organs. The heart of Pelophylax cf. bedriagae consisted of three chambers (two atria and one ventricle). Two atria were completely separated, however the ventricle were undivided. When looking dorsally on the heart, thin-walled sinus venosus was observed. The sinus venosus is responsible for initiating the heart beat and receives venous blood coming from caput, anterior legs, and body that then flows to the right atrium. Pacemaker cells and ganglion cells were main cells of the sinus venosus. The layer of the heart wall consisted of epicardium, myocardium and endocardium. The epicardium was the outer layer of heart. The myocardium was medium layer which was composed of an outer compact layer and inner trabecular layer. Ventricular trabeculae were lined by a thin layer of endocardial endothelium. The inner trabecular layer of ectothermic vertebrates is accepted as homologous to the Purkinje network. The atrioventricular valves were composed of loose connective tissue.