There is strong evidence that autonomic imbalance plays an important role in progression of heart failure. Analysis of heart rate variability (HRV) has achieved substantial acceptance as a noninvasive method for the assessment of autonomic tone. The purpose of this investigation was to study HRV in an experimental model of heart failure using cardiomyopathic (BIO TO.2) hamsters. Animals showed an autonomic imbalance of cardiac control that seems due to attenuation of parasympathetic activity and an enhanced sympathetic tone. The reduction of parasympathetic activity in BIO TO.2 hamsters is suggested by (a) the reduction of the high-frequency (HF) spectrum, and (b) the lack of atropine to generate a response. The increased sympathetic activity is indicated by (a) the decreased time-domain indexes, (b) the increased LF/HF ratio of the power spectrum, and (c) the alteration of HRV indexes induced by propranolol. These results support the notion that in heart failure, there is a similar autonomic imbalance in both human and hamster and suggest that the cardiomyopathic hamster is a suitable experimental model for studying the involvement of the autonomic nervous system in the progression of heart failure.