OBJECTIVES: To evaluate the parasympathetic modulation in elderly inpatients with major depressive disorder (MDD) before and after electroconvulsive therapy (ECT) using both linear and nonlinear methods of heart rate variability (HRV) analysis. METHOD: A measure of local dimensional complexity (pointwise correlation dimension, PD2), as well as spectral analysis measures (LF, low-frequency range; HF, high-frequency range) were calculated for the heart rate time series of 10 elderly inpatients with MDD (70+/-7 years) before and after ECT. Hamilton Depression Rating Scale (HAM-D) was evaluated concomitantly. RESULTS: Only the responders to ECT (n=7; >or=50% reduction in HAM-D) exhibited a significant increase in PD2 (P=.0035), which showed a tendency towards a correlation with symptom improvement (r=.73, P=.06). Spectral analysis measures did not show a significant difference after ECT. CONCLUSION: Elderly patients with MDD, who respond to ECT, might show increased vagal modulation. Since nonlinear HRV measures have been shown to be reduced by aging, similar to cholinergic deficit, they might shed light on the increased risk for cardiac mortality in depression.