Canine myocardium subjected to low-flow ischemia has been studied to identify the interactions that develop between the microtubule-based cytoskeleton and the stress protein, HSC73, in viable cardiomyocytes revealing disrupted myofibrils. "Moderate" or "severe" low-flow ischemia was produced in chronically instrumented dogs by reducing circumflex coronary flow by 50% for 2 hours or by 75% for 5 hours. Electron and immunofluorescence microscopy demonstrated either partial or nearly complete depolymerization of the inter-myofibrillar microtubules in areas of myofibril disruption. The perinuclear microtubule girdle and centrosomal tubulin arrays appeared to remain intact following low-flow ischemia. HSC73 was distributed throughout the sarcoplasm and in perinuclear regions of normal myocytes but inter-myofibrillar microtubules were only minimally labeled for the stress protein. In cardiomyocytes displaying myofibril disruption, HSC73 co-localized with intact but not disrupted microtubules and with perinuclear and centrosomal tubulin. High molecular weight tubulin-HSC73 complexes could be isolated from more severely ischemic tissue. These results suggest that HSC73 directly interacts with tubulin and may protect microtubule integrity and limit myofibril disruption during reversible low-flow ischemia.