The heart wall of frog composed of epicardium, myocardium and endocardium. The myocardium is composed of branched and striated yet involuntary cardiac muscles which contracts and relax rhythmically at a fixed rate. The fibres of the self excitatory and conducting muscle of the heart are of three types-nodal fibres, transitional fibres and Purkinje fibres.
In frog heart, a number of muscular ridges called columnae carnae projected from the wall of ventricle into its cavity, dividing the peripheral part of the cavity into a number of pockets.