Dilated cardiomyopathy is a disease that is characterized by the expansion of both left and right heart chambers, by decreased contractility and systolic dysfunction. Dilated cardiomyopathy leads to lower quality of life of dogs and their death. Permanent therapy by the drugs of angiotensin converting enzyme inhibitors class given to the dogs with dilated cardiomyopathy, has a beneficial effect on the course of chronic cardiovascular disease.

Enalapril is a medicine that has influence on the renin-angiotenzine system. In animals enalapril is hydrolyzed with formation of active metabolite – enalaprylate. Last inhibits angiotensin-converting enzyme blocks the transformation of angiotensin I to angiotensin II. The block of angiotensin-converting effect is accompanied by antihypertensive effect associated with peripheral vasodilation, by decreased blood concentration of angiotensin II and aldosterone, by inhibition of pressor (sympathoadrenal) and by activation of depressor body systems (kallikrein- kinine and prostaglandins), by increased secretion of endothelin. Enalapril causes a gradual decrease in systolic and diastolic blood pressure without changes in heart rate, reduces left ventricular hypertrophy, improves coronary circulation, increases myocardial resistance to hypoxia and reduces the incidence of dangerous ventricular arrhythmias. Enalapril increases renal blood flow, improves kidney function.

The study is aimed at investigation of the efficiency of monotherapy with enalapril in dogs with initial stages of dilated cardiomyopathy.

Dilated cardiomyopathy in dogs was diagnosed considering anamnesis, clinical examination, instrumental and laboratory studies on the criteria of M.S Miller et al., 1989. In the experiment was used enalapril maleate (ENAP, Tab. 5,0 or 10,0 mg number 20. "KRKA dd, Novo mesto", Slovenia). It was prescribed in an initial dose of 0,125 mg/kg, which gradually (every 7–14 days) was increased to 0,5 mg/kg, 1–2 times a day. Enalapril therapy was a lifelong treatment in dogs with dilated cardiomyopathy.

Efficacy of treatment was divided into three stages (after 1, 3 and 6 months) using general clinical methods, electro and echocardiography, morphological and blood biochemical parameters.

Statistical calculations were done by the tests of the Shapiro-Wilks, Mann-Uitni and Wilcoxon. The difference between the experimental groups was considered significant at p<0,05, p<0,01, p<0,001.

Therapeutic efficacy was evaluated in 34 dogs with dilated cardiomyopathy at initial stages (HSSN I–II functional class). The dogs were divided into 2 groups, in particular: I (n=7) – animals which owners refused to provide treatment; II (n=27) – animals which ran enalapril monotherapy. Efficacy of treatment was assessed by the following indicators: life expectancy, the dynamics of the disease, the body temperature, heart rate, respiratory rate movements, the rate of filling with blood capillaries, P-wave duration of interval PQ and QT, complex QRS, end-diastolic volume, end-systolic volume, ejection fraction of the left ventricle, the anterior- posterior size of the left atrium, hemoglobin concentration, erythrocyte count and white blood cell count, erythrocyte sedimentation rate, the activity of alanine and aspartate aminotransferase.

Continuous treatment by enalapril in dogs with dilated cardiomyopathy at initial stages (chronic cardiovascular failure and II functional classes ) at a daily dose of 0,5 mg/kg contributed to the increase in life expectancy, general stabilization of the clinical condition, reduce of heart rate, frequency of respiratory movements and speed of filling the capillares by blood.

In the treatment of sick dogs with dilated cardiomyopathy serum urea and creatinine decreased that points to nefroprotectional properties of enalapril. The activity of alanine and aspartate aminotransferase in the serum of blood in the dogs with dilated cardiomyopathy didn’t change in the course of their enalapril treatment that tell about lack of hepatoxical properties in this medicine.

Perspective direction for the future researches is to study the effectiveness of treatment in dogs with cardiomyopathy, a combination of enalapril with losartan.

Key words: dogs, dilated cardiomyopathy, heart failure, treatment, enalapril.