Aim. To study the activity of lysosomal cysteine proteases (cathepsins L, H) and acid phosphatase, changing of permeability, stability of myocardial lysosomal membranes in rats in experimental expressed hyperhomocysteinemia model, and while administering L-arginine and carnitine. Methods. The study was performed on male Wistar rats kept on standard vivarium conditions divided into three control and three experimental groups of 8 animals each. Experimental samples were administered methionine, or combination of L-arginine and carnitine with methionine. The level of serum homocysteine was measured by ELISA. Cathepsin L and H activity was detected by spectrofluorimetric method. Acid phosphatase activity was recorded using the «end point» method. Results. In the model of expressed hyperhomocysteinemia the increase of cathepsin H total activity due to both lysosomal and nonlysosomal fractions was found. These changes were observed along with the general increase of lysosomal membranes permeability. When correcting hyperhomocysteinemia with L-arginine and carnitine a decrease of cathepsin L and H levels was noted as well as positive effect on the myocardial lysosomal membranes stability. Conclusion. Expressed hyperhomocysteinemia is accompanied by statistically significant increase of both lysosomal and cytoplasmic fractions of the cathepsin H activity, indicating the lysosomal membranes permeabilisation phenomenon; L-carnitine and arginine correct hyperhomocysteinaemia effects, leading to cathepsin L and H reduced activity and having a stabilizing effect on the lysosomal membranes of cardiomyocytes.