MMP9 and infection: 2004). In subacute CVB3 myocarditis on day 7 p.i. cardiac MMP‐9 activity as well as MMP‐9/MMP‐2 activity ratio were significantly up‐regulated in both WT and APN‐KO mice compared to baseline levels. However, the infection‐induced up‐regulation of MMP‐9 activity and MMP‐9/MMP‐2 actvity ratio was significantly attenuated in hearts of APN‐KO mice, indicating that systemic APN deficiency attenuates up‐regulation of cardiac MMP‐9 expression in inflammatory heart disease (Fig. 6A, respectively).