Platelet activating factor (PAF) and other lysolipids are released during conditions of ischemia/reperfusion. We have previously provided evidence in isolated mouse heart preparations (Langendorff) that PAF dose dependently affects heart function. The aim of the study was to determine the involvement of the PAF-receptor (PAFR) and nitric oxide in the regulation of the hemodynamic responses during PAF application potentially mediated via cGMP and IP₃/diacylglycerol signaling. In isolated mouse heart preparations increasing concentrations of PAF (0.1, 0.5 and 1 mM PAF; each continuously infused over 20 min) resulted in an early positive inotropic effect (0.1 mM after 20 min; left ventricular systolic developed pressure (LVSDP) from 747 to 1003 mmHg, coronary flow (CF) from 15.72.3 to 22.62 ml/(min*g) and reversed in a negative inotropic effect (0.5 mM after 20 min; LVSDP from 7810 to 584 mmHg and in CF from 252 to 191 ml/(min*g)). Potential involvement of PAFR was tested in a group of PAFR deficient mice..The PAF response was blunted (rise in systolic pressure about 25 % and coronary flow 26 %) and shifted to higher concentrations (max. positive inotropic response after 15 min 0.5 mM PAF). To test the involvement of nitric oxide pharmacological block (NG-monomethyl-L-arginine, L-NMMA 100 mM) of nitric oxide synthases (NOS) and genetically eNOS deficient mice were employed. In both groups the positive inotropic effect of PAF was strongly inhibited (by 85 % in L-NMMA group and 72 % in eNOS-/- group). Similarly the rise in CF was blunted (by 94 % in L-NMMA group and 56 % in eNOS-/- group). From this data we conclude that the inotropic response is partly mediated via PAFR and NO signaling. Further studies on murine cardiomyocytes (HL-1) shall provide information about PAF signaling and calcium homeostasis on the cellular level.