&NA;A case report of fatal spontaneous dissection of the distal left circumflex coronary artery in a 37‐year‐old postpartum female is presented. Samples of arterial wall from this patient and from six other postpartum females who died of unrelated causes were examined by light (LM), scanning electron (SEM), and transmission electron (TEM) microscopy. Morphological changes to explain the recognized predisposition of this cohort to coronary artery dissection were sought. The origin of the dissection was demonstrated by serial LM sections to be in midmedia with no intimal extension. The predominant plane of dissection was the junction of media and adventitia. Sarcolemmal blebbing and accumulation of amorphous intercellular material were demonstrated at the dissection site by SEM but were not seen elsewhere in the affected heart or in any of the six control hearts. These changes could not be distinguished by TEM from prolonged ischemic injury. There was no accumulation of eosinophilic leukocytes in the vessel wall or adventitia, and adventitial mast cells were not consistently more frequent than in the controls. No increase of stainable intramural mucopolysaccharides was seen in the fatal case. The results indicated no generalized arterial change in postpartum coronary arteries to account for the increased frequency of dissection. A focal degenerative process remains the most likely possibility.