“…Periodic stimulation applied at a high rate can lead to a variety of periodic and aperiodic rhythms, including alternans (a rhythm in which there is a beat-to-beat alternation in one or more action potential parameters) and ventricular fibrillation (Savino & Valentinuzzi, 1988). Within the last decade, the identification of the onset of ditterent forms of alternans with a period-doubling bifurcation has been made in several different cardiac preparations (Guevara et ai., 1981(Guevara et ai., , 1984(Guevara et ai., , 1989(Guevara et ai., , 1990Adam et al, 1982Adam et al, , 1984Goldberger et at, 1984;Guevara, 1984;Chialvo & Jalife, 1987;Smith et al, 1988;Hescheler & Speicher, 1989;Savino et al, 1989;Chialvo et al, 1990). In many of these reports, the alternans is often seen just prior to the phase of induction of irregular rhythms, including ventricular fibrillation.…”