The characteristics and underlying mechanisms of new-onset ventricular arrhythmia during pregnancy have not been adequately investigated. We studied 11 pregnant women aged 35.4 +/- 3.1 years who experienced new-onset ventricular arrhythmias during pregnancy. The onset of their first episode of ventricular arrhythmia was distributed equally over the 3 trimesters. Ventricular premature contractions (VPCs) and ventricular tachycardia (VT) exhibited a monomorphic configuration in all patients; in 8 (73%) they originated from the right ventricular outflow tract. The frequency of VPCs decreased by more than 95% in 83% of the patients; couplets and VTs disappeared completely in all patients during the postpartum period. All parameters of heart rate variability were significantly lower during pregnancy than postpartum (P < .05). QT and QTc intervals were normal during pregnancy in all patients. The slope and the intersect of the QT/RR relationship obtained from Holter ECGs were not significantly different during pregnancy and in the postpartum period. New-onset ventricular arrhythmias in pregnancy manifest characteristics similar to those of idiopathic VT. Our findings suggest that various hemodynamic and neurohormonal changes associated with pregnancy play an important role in ventricular arrhythmogenesis.