Infarct reducing effect of UP with blockade of KATP channels during preconditioning. HMR-1098 (6 mg kg−1) or 5-HD (10 mg kg−1) was given intravenously simultaneously with saline or U50,488 H (10 mg kg−1). After 24 h, the heart was removed, perfused and then subjected to I/R. n=7 in CON and UP groups. Values are expressed as mean±s.e.m. **P<0.01 vs CON, #P<0.05 vs UP, ##P<0.01 vs UP.