AbstractThe direct effects of platelet activating factor (PAF) (2.5 nM) on isolated guinea pig heart were studied: first, on Langendorff model perfused hearts, using the radiolabelled microspheres technique, we found that PAF reduced the myocardial flow homogenously. Secondly, using isolated “working” heart preparations, the direct effects of PAF on the coronary and aortic flows, heart rate, and systolic ejection volume were evaluated. PAF markedly reduced coronary and aortic flows. Systolic ejection volume (SEV) was significantly decreased and the reduction, which was maximal at 3 min, persisted at 20 min. Some of the direct cardiac effects of PAF were antagonized by addition of GBE to the medium (10 mg/l). These data demonstrate the direct effects of PAF on cardiac function. The possible of PAF in the mediation of the episodes of coronary spasm may be sugges