CFB and ischemia: To determine the source of the fB which contributed to post-I/R myocardial necrosis, fB-/- mice (n = 4) were re-constituted i. v. with WT serum to provide an extracellular source of fB (i.e. no local production) and subjected to myocardial IR as above (1 h ischemia / 24 h reperfusion).