Protocols of remifentanil administration. Sham, sham operation group; I/R group, myocardial ischemia/reperfusion group; R-post, postconditioning of remifentanil group; R-post +Ace, postconditioning of remifentanil plus acetazolamide group; R-post +AC, postconditioning of remifentanil plus antagonist compounds; R-post +AV, postconditioning of remifentanil plus arginine vasopressin.