In a postmortem study of the hearts of two young women who died suddenly and unexpectedly, we found a remarkably similar and distinctive ganglionitis, predominantly in the region of the sinus node. Both women had ventricular fibrillation at the time of collapse. Vesicular neuritis and older neural degeneration were present in other regions of the heart. Except for focal fibromuscular dysplasia of the sinus node artery and atrioventricular node artery of one heart, there was no other significant anatomic abnormality in either heart. The functional significance of this cardiac ganglionitis is unclear, but its location in and around the conduction system makes it a possible cause of the fatal electrical instability. Recognition that ganglionitis of the heart may be associated with sudden death should stimulate a number of additionally useful studies.