ABSTRACTHeat‐induced changes in myofibrillar protein solubility were studied in samples of at‐death and postmortem bovine logissimus heated at 45°, 50°, 55°, 60°, 70° and 80°C. Myofibrillar proteins were extracted with strong salt solution after the removal of sarcoplasmic proteins for each heat treatment. Changes in myofibrillar protein solubility were determined by using SDS‐polyacrylamide gel electrophoresis. The proteins of thick and thin filaments and Z‐disks reacted differently to heat and postmortem aging time. Alpha‐actinin was the most heat labile and became insoluble at 50°C. Next, heavy and light chains of myosin became insoluble at 55°C. Actin, tropomyosin and troponin were more heat resistant, however, inasmuch as actin was insoluble between 70 and 80°C and tropomyosin and troponin became insoluble above 80°C. That the 30,000‐dalton component was more intense after heating suggests that calcium activated factor (CAF) activity is stimulated during heating. This further suggests that the effect of CAF on heated muscle is additive to its tenderization effect on p