We have previously demonstrated that diminazene aceturate (DIZE), a putative angiotensin 1-7 converting enzyme activator, protects rats from monocrotaline (MCT)-induced pulmonary hypertension (PH). The present study was conducted to determine if the beneficial effects of DIZE are associated with improvements in autonomic nervous system (ANS) modulation. PH was induced in male rats by a single subcutaneous injection of MCT (50 mg/kg). A subset of MCT rats were treated with DIZE (15 mg/kg/day) for a period of 21 days, after which the ANS modulation was evaluated by spectral and symbolic analysis of heart rate variability (HRV). MCT administration resulted in a significant (P<0.001) increase in the right ventricular systolic pressure (62 +/- 14 mmHg) when compared with other experimental groups (Control: 26 +/- 6; MCT + DIZE: 31 +/- 7 mmHg), while DIZE treatment was able to decrease this pressure. Furthermore MCT-treated rats had significantly reduced total power of HRV than the controls. On the other hand, although not significant, a trend towards increased HRV was observed in the MCT + DIZE group (Control: 108 +/- 47; MCT: 12 +/- 8.86 and MCT + DIZE: 40 +/- 14), suggesting an improvement of the cardiac autonomic modulation. This observation was further confirmed by the low-frequency/high-frequency index of spectral analysis (Control: 0.74 +/- 0.62; MCT: 1.45 +/- 0.78 and MCT + DIZE: 0.34 +/- 0.49) which showed that DIZE treatment was able to recover the ANS imbalance observed in the MCT-induced pulmonary hypertensive rats. Collectively, our results demonstrate that MCT-induced PH is associated with a significant increase in sympathetic modulation and a decrease in HRV, which are markedly improved by DIZE treatment.