A significant amount of myocardial damage during a myocardial infarction (MI) occurs during the reperfusion stage, termed ischaemia/reperfusion (I/R) injury, and accounts for up to 50% of total infarcted tissue post-MI. During the reperfusion phase, a complex interplay of multiple pathways and mechanisms is activated, which ultimately leads to cell death, primarily through apoptosis. There is some evidence from a lupus mouse model that lupus IgG, specifically the antiphospholipid (aPL) antibody subset, is pathogenic in mesenteric I/R injury. Furthermore, it has previously been shown that the immunodominant epitope for the majority of circulating pathogenic aPLs resides in the N-terminal domain I (DI) of beta-2 glycoprotein I (β2GPI). This study describes the enhanced pathogenic effect of purified IgG derived from patients with lupus and/or the antiphospholipid syndrome in a cardiomyocyte H/R in vitro model. Furthermore, we have demonstrated a pathogenic role for aPL containing samples, mediated via aPL–β2GPI interactions, resulting in activation of the pro-apoptotic p38 MAPK pathway. This was shown to be inhibited using a recombinant human peptide of domain I of β2GPI in the fluid phase, suggesting that the pathogenic anti-β2GPI antibodies in this in vitro model target this domain.