The role of cytoskeletal damage in the disruption of the plasma membrane observed during myocardial ischemia has been studied using antibodies to vinculin to identify changes in the distribution of this membrane associated cytoskeletal protein. Vinculin is a component of the cytoskeletal attachment complex between the plasma membrane and the Z-line of the underlying myofibrils. The effects of varying periods of total ischemia on the localization of vinculin were assessed by immunofluorescence and evidence of membrane disruption was evaluated by electron microscopy. Thin tissue slices prepared from the ischemic tissue were incubated in oxygenated Krebs-Ringer phosphate buffer at 37± C to assess inulin permeability, ultrastructure, and any changes in the distribution of vinculin associated with incubation. The previously reported costameric pattern of vinculin staining was observed in longitudinal sections of control myocardium, myocardium subjected to 60 minutes of total ischemia, and myocardium subjected to 60 minutes of ischemia followed by 60 minutes of incubation in oxygenated media. Electron microscopy and inulin permeability measurements confirmed that plasma membrane integrity was preserved under these conditions. However, when the duration of total ischemia was extended to 120 minutes or longer, there was a progressive loss of vinculin staining along the lateral margin of myocytes. This change correlates with the appearance of subsarcolemmal blebs and breaks in the plasma membranes observed by electron microscopy and confirmed by the increase in inulin permeability observed in tissue slices. These data demonstrate that there is a close association between cytoskeletal damage and plasma membrane disruption and suggest that breakdown of the cytoskeletal scaffold underlying the plasma membrane may be responsible for weakening the plasma membrane and allowing it to rupture as a consequence of cell swelling during ischemia.