Several investigators have shown signs of possible sympathetic but not parasympathetic reinnervation in heart transplanted patients. Spectral analysis of heart rate and blood pressure variability is a noninvasive tool appropriate to detect a functional autonomous reinnervation to the heart. In a follow-up study, 13 patients after heart transplantation (HTx) were investigated, mean age 50.6+/-8.5 years, 18 healthy volunteers were selected as control group. For each patient two recordings were performed which took part 14+/-5 months respectively 42+/-8 months after HTx. ECG and systolic blood pressure (SBP) have been recorded simultaneously for 5 min in supine position during controlled respiratory rate of 12 or 15 cycles/min. No graft rejection has been detected in the endomyocardial biopsy performed right after the recordings. Power spectral densities (PSD) were calculated for the beat-to-beat time series of RR-intervals (distance of two following QRS complexes) and SBPs. The area of PSD in the range of 0.05-0.17 Hz was defined as low frequency (LF) and that of 0.18-0.35 Hz as high frequency (HF). LF and HF are indicative of efferent sympathetic respectively parasympathetic activity at the sinus node. A significant increase of LF (226%) and HF (213%) during a mean period of 28 months could be found. No differences were to be shown for systolic blood pressure variability. Previous findings confirm that LF band increases 4 years after transplantation, suggesting a possible sympathetic reinnervation of the heart. On the other hand an increase of the HF band also suggests a parasympathetic reinnervation.