Established from the embryonal (stage 52/53) normal heart endothelium (tadpole heart) of a South African clawed frog (Xenopus laevis Daudin) in 1979; cells were described to synthesize factor-VIII-related antigen (AHG-a.p.), fibronectin and laminin and to be tetraploid (72 +/-5, 2N = 36)