ID1 and Endocardial fibrosis: Conversely, aged 12–14 month old Id control mice (Id1F/−Id3−/−) develop signs of cardiac disease characterized by endocardial fibrosis reminiscent of early Id cDKO pathology, suggesting that Tie2Cre mediated ablation of Id compensation results in acceleration of cardiac pathology as Id cDKO hearts typically present with fulminant pathology by 6 months of age.