Stability of PF4-heparin complexes. SEC-HPLC of PF4-heparin complexes as in Figure 1. (A) Chromatograph of PF4-heparin complexes at a PHR of 1:1. (B) Rechromatograph of SC from (A) after 24 hours of incubation at 37°C. (C) Rechromatograph of ULCs from panel A after 1 or 24 hours of incubation at 37°C. (D) Rechromatograph of ULCs from panel A after incubation with excess heparin as described in “Results.”