A synthetic heme analog that selectively inhibits HO-1 (Ki = 11 nM) over HO-2 (IC50 = 7.5 µM); weakly inhibits eNOS and soluble guanylyl cyclase (IC50s = 35 and 30 nM, respectively); prevents hyperbilirubinemia in neonates by blocking HO-1 activity that increases postnatally.