The aim of this study was to identify the main proteins associated to the cardiac sarcoplasmic reticulum (SR) and involved in the calcium homeostasis. Horse cardiac tissue is characterized by the action potential duration (APD) (0,6-1,0 s) and resting heart rate (30-40 beats/min), which are significantly different from humans and smaller mammals. By immunofluorescence techniques we have described the expression of ryanodine receptor (RyR2), sarco(endo)plasmic reticulum Ca-ATPase (SERCA2) and histidine-rich Ca-binding protein (HRC). The expression of HRC in atrial and ventricular tissues was also confirmed, at the mRNA level, by PCR experiments.