Conventional in vitro cell cultures are relatively available and have been widely used in explaining many mechanisms, but their simple construction is not directly applied to the in vivo environment. A possible solution to overcome this problem is special in vitro model maintained with cardiac slices. Slices show a preserved architecture, multi-cellularity and physiology of the heart tissue. This approach creates a bridge between the gap in cellular and in vivo studies. This study demonstrated that it is possible to find protein biomarkers between rat myocardial slices which were stretched to sarcomere lengths (SL) within the physiological range of 1.8–2.4μm and slices cultured without electromechanical stimulation and with fresh myocardial slices.