While the translation of ischemic preconditioning to clinical application remains unrealistic for patients with acute myocardial infarction (AMI), recent research in ischemic postconditioning opens new opportunity for potentially accessible clinical treatment for AMI. Reperfusion injury salvage kinase (RISK) pathway has been implicated in the postconditioning for infarct-size (IS) reduction [
1,
2]. Among several potential mechanisms, Akt activation has been implicated as one of the key signaling pathways underling postconditioning mediated heart protection [
1,
2], although species difference has been reported [
3]. The mammalian heart possesses adrenopeptidergic neuroparacrine system consisting of intrinsic cardiac adrenergic (ICA) cells [
4‐
6]. ICA cells synthesize and release epinephrine and calcitonin gene-related peptide (CGRP), stimulating myocardial β
2-adrenoreceptor (β
2-AR) and CGRP-receptors [
5,
6], both of which being coupled to the adenylate cyclase-cAMP-dependent signaling pathway [
7‐
9]. Concomitant stimulation of cardiac β
2-AR/CGRP-receptors before ischemia or at the beginning of the reperfusion confers robust IS-reduction [
10]. This adrenopeptidergic signaling is mediated through the activation of cAMP-dependent PKA [
10] which, in turn, activates Akt, a powerful antiapoptotic signaling pathway [
1,
2,
11,
12]. It is conceivable that medications sharing similar distal signaling mechanisms of β
2-AR/CGRP-receptors may provide alternatives for the receptor-mediated cardioprotection. For instance, direct myocardial PKA activation with a phosphodiesterase (PDE) III inhibitor milrinone at reperfusion may confer equivalent cardioprotection to that conferred by β
2-AR/CGRP-receptor stimulation
, since milrinone is known to activate PKA [
13,
14]. High dose of β
1-AR blocker esmolol given at the onset of reperfusion reduces LV-IS [
15]. This cardioprotective effect is likely mediated, in part, through the enhanced β
2-AR signaling promoting myocyte survival [
11,
12], since at early reperfusion, there is >100 fold increase in myocardial interstitial epinephrine release [
16] exerting unopposed myocardial β
2-AR stimulation in the presence of β
1-AR blockade. Although, it has been reported that intra-ischemic PKA activation with milrinone reduces right ventricular IS in dogs [
17], it has not been demonstrated whether intra-ischemic/reperfusion therapy with milrinone reduces LV-IS. Furthermore, the mechanism underlying post-ischemia milrinone-induced heart protection has not been elucidated. We have hypothesized that cardiac PKA activation with the selective β
1-AR blocker esmolol in combination with milrinone at late-ischemia/early reperfusion decreases LV-IS. The present study had the following objectives: to determine if: 1) LV-IS can be additively reduced by cardiac PKA activation with combination therapy of esmolol + milrinone delivered at the beginning of reperfusion, in a manner dependent of PKA and Akt activation; 2) myocyte death rates can be reduced by intra-ischemic treatment with esmolol + milrinone in vitro, 3) combination therapy with esmolol + milrinone additively enhance myocardial PKA and PKA-dependent Akt activation; and 4) esmolol + milrinone-induced Akt activation results in reduced myocyte apoptosis during ischemia/reperfusion.