Abnormalities in the excitation-contraction (EC) coupling of slow-twitch muscle seem to explain the slowing and increased fatigue observed in congestive heart failure (CHF). However, it is not known which elements of the EC-coupling that might be affected. We hypothesize that the temperature sensitivity of contractile properties of the soleus muscle might be altered in CHF possibly because of alterations of the temperature sensitivity of intracellular Ca²⁺ handling. We electrically stimulated the in situ soleus muscle of anaesthetised rats that had six week post-infarction CHF using 1 and 50 Hz and using a fatigue protocol (5 Hz stimulation for 30 min) at 35, 37 and 40 °C. Ca²⁺ uptake and release were measured in sarcoplasmic reticulum vesicles at various temperatures. Contraction and relaxation rates of the soleus muscle were slower in CHF than in Sham at 35 °C, but the difference was almost absent at 40 °C. The fatigue protocol revealed that force development was more temperature sensitive in CHF, whereas contraction and relaxation rates were less temperature sensitive in CHF than in Sham. The Ca²⁺ uptake and release rates did not correlate to the difference between CHF and Sham regarding contractile properties or temperature sensitivity. In conclusion, the discrepant results regarding altered temperature sensitivity of contraction and relaxation rates in the soleus muscle of CHF rats in comparison to Ca²⁺ release and uptake rates in vesicles indicate that the molecular cause of slow-twitch muscle dysfunction in CHF is not linked to the intracellular Ca²⁺ cycling.