Abstract—Adecreased exercise tolerance is a common symptom in patients with congestiveheart failure (CHF). This decrease has been suggested to be partly due toaltered skeletal muscle function. Therefore, we have studied contractilefunction and cytoplasmic free Ca2+concentration([Ca2+]i,measured with the fluorescent dye indo 1) in isolated muscles from rats inwhich CHF was induced by ligation of the left coronary artery. The resultsshow no major changes of the contractile function and[Ca2+]ihandling in unfatigued intact fast-twitch fibers isolated from flexordigitorum brevis muscles of CHF rats, but these fibers were markedly moresusceptible to damage during microdissection. Furthermore, CHF fibersdisplayed a marked increase of baseline[Ca2+]iduring fatigue. Isolated slow-twitch soleus muscles of CHF rats displayedslower twitch contraction and tetanic relaxation than did muscles fromsham-operated rats; the slowing of relaxation became more pronounced duringfatigue in CHF muscles. Immunoblot analyses of sarcoplasmic reticulum proteinsand sarcolemmaNa+,K+-ATPaseshowed no difference in flexor digitorum brevis muscles of sham-operatedversus CHF rats. In conclusion, functional impairments can be observed in limbmuscle isolated from rats with CHF. These impairments seem to mainly involvestructures surrounding the muscle cells and sarcoplasmic reticulumCa2+pumps, the dysfunction of which becomesobvious duringfatigue.