improved functional recovery of the isolated rat heart after 24 hours of hypothermic arrest with a stable prostacyclin analogue zk 36 374 prostacyclin pgi2 can protect the heart against ischemia ie it can reduce myocardial damage 9 10 pgi2 protects the myocardium in vivo by preventing platelets from clumping and by dispersing preformed platelet aggregates 114 however also in the absence of platelets pgi2 was shown to protect the myocardium against ischemia at concentrations that did not affect smooth muscle tone in the vessel wall 2 this protective effect of pgi2 in vitro might be related to a stabilization of cell membranes in adrenergic nerve endings and hence to the prevention of ischemiainduced catecholamine release 13 the instability of pgi2 both in vitro and in vivo limits its application during long ischemic periods recently a stable prostacyclin analogue zk 36 374 was demonstrated to have several prostacyclinmimetic activities both in vitro and in vivo 1112 in this communication we report upon the beneficial effect of this stable prostacyclin analogue at a low concentration 4 nm on the extent of ischemic damage on the recovery of myocardial function and on the occurrence of arrhythmias in the isolated rat heart after 24 h hypothermic cardiac arrest