A pacing system, which is particularly suitable for implantable leadless pacemakers, applies passively-balanced voltage-based pacing pulses, and periodically performs capture verification (evoked response detection) by following a pacing pulse with a current-based active balancing pulse, and then measuring any evoked response provoked by the pacing pulse. The active balancing pulse reduces residual charge on the electrodes used for pulsing, and thereby reduces polarization artifacts that could obscure measurement of the evoked response at the electrodes. The amplitude and pulse width of the active balancing current pulse are defined by measurements made in a few preceding pulses. The pacemaker preferably detects indicia of cardiac contractility, and performs capture verification only when contractility indicates that the patient is physically inactive and emotionally stable.