Using light, transmission (TEM) and scanning (SEM) electron microscopy, cocaine-induced defects were observed in hamster atria. Compared with controls, the treated atria from neonates show endocardial and myocardial damages as the atrial walls thicken. SEM micrographs show intensive blebbing, damage and incomplete coverage of myocardium by the endocardial endothelium. TEM data demonstrate blebs, thinning, and other endothelial cell injuries and complement the SEM findings. Areas of endothelial sloughing may facilitate the formation of luminal and mural thrombi as noticed in many neonatal atria. Adjacent subendocardial myocardial cells display contraction bands, swellings, and vacuolizations. Local and large areas of damaged myocardial cells are observed in the subendothelial spaces; they contact fibroblasts squeezed or intercalated between the subendocardial spaces and the basal side of damaged endothelial cells. Many of these defects correspond to well-known ischemic changes. One can hypothesize that cocaine-induced defects appear to be linked to membranous alterations, including those associated with the endothelial cells of the endocardium
