Acute resistance exercise (RE) has been shown to reduce cardiac vagal control. Whether this would in turn affect QTc interval (an index of ventricular depolarization/repolarization) or heart rate complexity is not known. Heart rate variability (HRV), heart rate complexity (SampEn), and QT interval (rate corrected using Bazett, Fridericia, Hodges, and Framingham) were measured before and 5 min after an acute RE bout in twelve healthy young men. Normalized high frequency power of HRV (an index of cardiac parasympathetic modulation; HF (nu)), and SampEn were reduced following RE (p < 0.05). Bazett corrected QTc interval increased following RE (p < 0.05). Change in HF (nu) from rest to recovery was correlated with both change in SampEn (r = 0.51, p < 0.05) and change in QTc interval for each method of correction (r = - 0.67 to - 0.70, p < 0.05). Acute RE reduced HF spectral power of HRV and this was related to both reduced heart rate complexity and increased QTc length. Thus, during recovery from acute RE, there is prolongation of depolarization and repolarization of the ventricles concomitant with reduced cardiac irregularity, and this may be related to a reduction in cardiac vagal control.