[Frequency-dependent effects in an alternating electric field on an isolated frog heart].

An isolated frog heart placed in a special chamber with Ringer solution (pH 7.2) was stimulated by electric field at a frequency of 0.3-4.0 Hz with graphite electrodes immersed in the solution. Unusual resonance phenomena were observed during a progressive increase or decrease of the stimulation frequency: the amplitude of the mechanical responses of the preparation rose at multiple frequencies of stimulation, whereas the frequency of the responses remained unchanged.