PMN contribute to cardiac reperfusion injury. To do so, they must become adherent, a process attenuated by an intact endothelial glycocalyx (EG), normally 300 nm thick. Shedding of the EG should increase neutrophil adhesion. To evaluate the adherence of PMN in situ, 10⁶ human PMN were applied in 1 min to isolated perfused guinea pig hearts. We found that the basal adhesion (range 18–42%) depends on the individual blood donor. For a donor whose PMN showed a basal adhesion of 20% in the control group (n=7), adhesion was increased to about 35% (n=6) after pretreatment of hearts with heparinase (10 U in 10 min). 20 min of warm ischemia as well as 4h of cold ischemia also result in shedding of EG and a significantly increased adhesion of PMN (40%). For comparison, human umbilical vein endothelial cells (HUVEC) were cultivated in IBIDI m-slides. Electron microscopy showed a thickness of the glycocalyx of about 20–30 nm, <10% of "normal". The HUVEC were exposed to a constant flow of 1 ml/min and 10⁶ PMN labelled with calcein were infused. After fixation with formalin, adherent PMN were counted (fluorescence microscope). We found no significant difference in the number of adhesive PMN between the control group and HUVEC pretreated with 1.7 U heparinase. These results confer a protective role to the intact endothelial glycocalyx in situ in the coronary system. On the other hand, cultured HUVEC, a popular in vitro model, do not develop sufficient glycocalyx to influence PMN adhesion.