BACKGROUND: Transient left ventricular (LV) apical ballooning (AB) is characterized by a rapidly reversible, acute LV systolic dysfunction, triggered by physical or emotional stress. Despite observations strongly suggesting catecholamine-mediated myocardial stunning due to enhanced sympathetic activity, the early time course of heart rate variability (HRV) has not been described. METHODS: We prospectively enrolled 39 consecutive patients (median age = 68 years, range 35-85 years, 38 women) with LV AB. Indices of HRV were extracted from 24-hour ambulatory electrocardiograms on the day of hospital admission, on days 2 and 3, and 3 months after the hospitalization. RESULTS: Within 48 hours after hospital admission, the indices of HRV were markedly depressed (standard deviation of normal-to-normal [NN] intervals [SDNN] 89.6 +/- 19.9 ms; mean standard deviation of NN intervals for 5-minute segments [SDNNi] 37.8 +/- 6.2 ms; root mean square of consecutive difference of normal-to-normal intervals [rMSSD] 23.0 +/- 9 ms; standard deviation of the averages of NN intervals for all 5-minute segments [SDANN] 70.1 +/- 18.0 ms; geometric triangular index [TI] 23.7 +/- 5.9 ms), recovered in the subacute phase and had normalized at 3 months follow-up (SDNN 124.7 +/- 24 ms; SDNNi 47.1 +/- 5.7 ms; rMSSD 31.1 +/- 10.5 ms; SDANN 118.5 +/- 27 ms; TI 31.2 +/- 8 ms; all P < 0.05). Mean RR-interval increased from 845 +/- 121 ms on day 1, to 929 +/- 84 ms at 3 months (P=0.06). CONCLUSIONS: A marked depression of cardiac parasympathetic activity was observed in the acute phase of LV AB, followed by recovery of autonomic modulation between the subacute and the chronic phases. The rapid return of parasympathetic function may partially explain the favorable outcomes of patients presenting with LV AB.