Chaotic behavior in toad ventricle

We recorded monophasic action potentials with small suction electrodes from toad ventricles (Bufo arenarum) which were paced by pulses of slowly increasing frequency. Resulting time series, attractor reconstruction and spectral analysis gave a transition to disordered behavior which is compatible with Feigenbaum scenario (Physics Today, Dec. 83, p. 46). Subharmonic components (f/2, f/4) was systematically detected in the power spectra. The disordered solutions yielded a continuous spectrum which allowed their characterization. It has been conjectured that Feigenbaum's route can be a precursor of fibrillation in the mammalian heart. In such case, generalized ischemia due to to fall in blood pressure appears as an additional complication. Bufo arenarum does not have a coronary system; thus, this complication is minimized. Conclusion: Cardiac syncitium presents a chaotic behavior when driven at increasing rates.