OBJECTIVE: To examine differences in the spectral power content in neonates diagnosed with congenital diaphragmatic hernia (CDH) who survive or succumb. STUDY DESIGN: A case-series study design evaluated four neonates diagnosed with CDH, two of which were supported by extracorporeal membrane oxygenation (ECMO). The electrocardiogram signal was digitized at 1000 Hz and the Lomb periodogram was computed for the series of interbeat intervals. RESULTS: Neonates with CDH who survived had log total power values greater than 2. Those with CDH who did not survive had log total power less than 2, but generally exceeded 3 while they were supported by ECMO. CONCLUSIONS: Neonates who consistently displayed increasing total spectral energies had a better outcome than those whose spectral energies were low. Subjects who succumbed expressed the lowest values, suggesting that a frequency-based evaluation of HRV may be a sensitive prognosticator of outcome that requires further investigation.