Antibody-mediated rejection (AMR) of the cardiac allograft, formerly also termed vascular or humoral rejection, typically occurs in the absence of interstitial lymphocytic infiltrates that are characteristic of acute cellular rejection. Its pathological hallmarks include capillary endothelial activation and macrophage infiltration, as well as vascular immunohistochemical deposition of immunoglobulin and complement. Clinically, AMR occurs early post heart transplant and tends to recur, is harder to treat, and is associated with poor outcomes (Hammond et al., J Heart Transplant 8:430–443, 1989; Lones et al., J Heart Lung Transplant 14:151–162, 1995; Michaels et al., J Heart Lung Transplant 22:58–69, 2003; Casarez et al., J Heart Lung Transplant 26:114–119, 2007; Everitt et al., J Heart Lung Transplant 31:686–693, 2012; Ensley et al., Transplant Proc 23:1130–1132, 1991).