Heart rate variability (HRV) is often used to study disturbances in the autonomic nervous system. Respiratory related HRV is seen as an indicator of a working autonomic mechanism. However, sometimes a high HRV may be caused by non-autonomic mechanisms. This study investigated if the wavelet coherence could be used to study respiratory related fluctuations in heart rate. The wavelet coherence method was applied to two Familial amyloidotic polyneuropathy patients and one healthy control. The results showed that wavelet coherence is a promising method for studying respiratory related fluctuations in heart rate.