AV block after arsenic trioxide (As2O3) treatment for refractory acute promyelocytic leukemia is very rare. In this patient, the block was at A-H level and manifested with complete AV block and Wenckebach second-degree type 3:2 block. The junctional recovery time during complete AV block did not significantly prolong after administration of more arsenic trioxide. The effect of heart block of arsenic trioxide seemed reversible after the discontinuation of arsenic trioxide and was not correlated to the leukemic status as observed in this patient.