Remodeling of myocyte interconnections may be an important determinant of ventricular tachycardia in regions bordering healed infarcts. We used quantitative electron microscopy to characterize the distribution of gap junctions in 10 canine left ventricles 3-10 wk after coronary occlusion. In three normal canine left ventricles analyzed ultrastructurally, myocardial gap junctions were distributed anisotropically; gap junction profile length was significantly greater in the transverse than in longitudinal planes of section. In infarct border zone tissues, the normal anisotropic distribution was completely abolished and fewer gap junctions per unit intercalated disk length were observed. Analysis of individual gap junction profile length distributions revealed selective disruption of the largest gap junctions that collectively comprised only 9.6% of total junction profiles, but encompassed nearly 40% of aggregate gap junction length in the transverse plane of section. Three-dimensional reconstructions of myocyte interconnections by high resolution quantitative light microscopy of serial sections demonstrated a reduction in the number of cells connected by intercalated disks to a single myocyte from 11.2 +/- 1.0 in normal myocardium to 6.5 +/- 1.3 in border zone tissues (P less than 0.001). Connections of cells in primarily side-to-side apposition were reduced by 75%, whereas primarily end-to-end connections were reduced by only 22% (P less than 0.05). These alterations would disproportionately enhance axial resistivity in the transverse direction, potentially contributing to development of reentrant arrhythmias.