Atrial action potential duration (APD) has been shown to decrease with increasing distance from the sinoatrial node in several species, including humans. This gradient has been postulated to be cardioprotective by reducing repolarization gradients.This study tests the effect of the APD gradient on reentry initiation and characteristics.This study used a geometrically accurate atrial computer model to examine arrhythmogenic consequences of an APD gradient on reentry initiation by ectopic beats applied at several locations. As well, dominant frequency maps of any ensuing reentries were analyzed to determine how APD gradients affected rotor behaviour.When the APD gradient was increased, anatomic reentry that used the coronary sinus as a critical pathway was prevented, but initiation of functional reentry was unaffected. If a rotor did form, APD gradients led to more disorganized behaviour. For rotors circulating around the pulmonary veins, discrete interatrial coupling accounted for left atrium-right atrium frequency gradients, irrespective of an APD gradient.Gradients are protective against anatomic reentry but also increase the complexity of arrhythmias that arise.