The invention describes use of 5-amino-2, 3-dihydrophthalazine-1, 4-dione sodium salt for treatment of heart diseases, particularly myocarditis, as well as for treatment of pancreas diseases, particularly pancreas inflammatory states, and diabetes, and also use of the said sodium salt, optionally in combination with the lithium salt, for treatment of nervous system diseases, particularly Alzheimer disease, as well as psychic diseases, particularly depression syndromes and anxiety states.