Ectopic spiral wave sources--reverberators--were produced in pieces of rabbit atrium and ventricle by an induction of a single properly timed premature impulse. It was found that the cycle length (T) of the ectopic source gradually increased immediately after its appearance in atrial and changed a little bit after its appearance in ventricular tissue. Relationship between changes of T and refractorines of the heart tissues was investigated. The model is proposed which explains these changes of T by the cycle length dependence on the value of fast inward sodium current.

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