The atrioventricular (AV) conduction system in AV discordance remains unclear, especially in cases with complex cardiac anomaly. We report a case of accessory pathway reciprocating tachycardia in atrioventricular discordance (AVD) and mitral atresia with twin AV nodes. In this case, the anterior AV node was located along the atretic mitral valve. The anterior AV node was involved in tachycardia and the posterior AV node acted as a bystander during tachycardia. The anterior AV node in AVD can be located along the atretic mitral valve, and one of twin AV nodes might act as a bystander during AV reciprocating tachycardia.