Hibernating animals over the course of evolution developed an adaptive winter slipping mechanism which allows them to survive in the extreme condition of north. It is well known that adenosine and purine nucleotides act as regulatory compounds in the cardiovascular system. Purine nucleotides' level is higher in the heart of hibernators in comparison with nonhibernators. Effects of purine compounds on the heart of the hibernating animals are not sufficiently characterized. The aim of the present study is to investigate effects of purine compounds as adenosine, AMP, ADP-ribose and GMP (Sigma) on bioelectric activity of atrium and papillary muscle (PM) of the hibernating animal (ground squirrel Citellus undulates) and the rat. Action potentials (AP) were obtained with use of standard microelectrode technique. AP duration was estimated at the level of 50 % (APD50) and 90 % of repolarization (APD90) in the control experiments and in the presents of drugs (1×10^-5M). Purine compounds decreased APD50 and APD90 both in PM and atrium of hibernating ground squirrel. In ground squirrel PM adenosine, AMP, ADP-ribose and GMP decreased APD50 at 267 %, 238 %, 268 % and 265 %; APD90 at 133 %, 103 %, 123 %, and 134 %, respectively. In ground squirrel atrium adenosine and AMP decreased APD50 at 183 % and 103 % respectively; APD90 at 112 % and 92 %, respectively. ADP-ribose and GMP did not reduce APD. Effects of purine compounds in the rat heart were similar, except decrease of APD90 in ground squirrel PM was up to 2–2.5 fold less then that in the rat PM. This peculiarity may contribute to insusceptibility of ground squirrel myocardium to arrhythmias in presence of compounds that shorten APD (such as adenosine).