The aim of this study was to characterize the heat treatment-induced changes in electrophoretic patterns of myofibrillar proteins. The study was carried out on longissimus thoracis (LT) muscle from two pig lines (Galia and Redone). The following post mortem metabolic and meat quality parameters were determined: pH24h, lactate, residual glycogen, glycolytic potential and drip loss. Heat treatment at 100°C was applied for either 10 min or 30 min. SDS-PAGE electrophoresis was performed before and after cooking. The results showed that Galia-breed LT muscles had lower pH24h and higher residual glycogen, glycolytic potential and drip loss than Redone-breed LT muscle. We found different electrophoretic patterns between raw and cooked meat for each breed. Electrophoretic pattern profiles after heating showed a decrease in myosin (up to 50%) and actin (up to 40%) together with new bands of lower molecular weight (mainly at 80 kDa, 60 kDa and 25 kDa). The appearance of these new bands could be explained either by heating-induced myosin and actin band breakdown or by changes in protein solubility and extractability. Research is currently being led to identify these proteins and thus confirm these hypotheses.