['The purpose of this study was to examine the effects of cyclooxygenase (COX) deficiency on baseline functional characteristics and on recovery of left ventricular developed pressure (LVDP) after 20 minutes of global ischemia and 40 minutes of reperfusion in untreated and preconditioned hearts.', 'Compared with hearts from wild-type (WT) and COX-2(-/-) mice, baseline cardiac prostaglandin (PG) E(2) and 6-keto-PGF(1alpha) levels were significantly decreased in hearts from COX-1(-/-) mice. After ischemia, cardiac PGE(2) levels increased in WT, COX-1(-/-), and COX-2(-/-) mice (P<0.05). Recovery of function (LVDP) after global ischemia in hearts from COX-1(-/-) and COX-2(-/-) mice was significantly less than in WT hearts. Pretreatment of WT mice with indomethacin for 2 days before ischemia significantly decreased LVDP recovery; however, perfusion of WT hearts with indomethacin for 40 minutes before ischemia did not significantly alter LVDP recovery. Postischemic recovery of LVDP in COX-1(-/-) and COX-2(-/-) was unchanged by perfusion with 5 micromol/L PGE(2), PGD(2), PGF(2alpha), or carboprostacyclin. Hearts from COX-2(-/-) mice showed an increase in ischemic contracture compared with hearts from WT and COX-1(-/-) mice; however, hearts did not differ in intracellular pH, ATP, or inorganic phosphate during ischemia. Ischemic preconditioning significantly improved postischemic LVDP recovery in COX-1(-/-), COX-2(-/-), and WT mice.'] Do cyclooxygenase-1 and -2 knockout mice demonstrate increased cardiac ischemia/reperfusion injury but are protected by acute preconditioning?