Background Ischaemia and reperfusion injury remains a critical issue in many clinical contexts, especially cardiovascular surgery. Our previous work (1) using normal and diseased adult rat heart has shown that sequential activation of Protein Kinase A (by isoprenaline (Iso)) followed by activation of Protein Kinase C (with adenosine (Ade)) confers marked protection against ischaemia/reperfusion injury. Purpose The protective effect of this intervention in the immature heart against ischaemia/ reperfusion injury is unknown. The aim of this work was to investigate the cardioprotective efficacy of this novel intervention during postnatal myocardial development. Methods Hearts from 14-day postnatal (interventions n=6, controls n=5) and from adult male (interventions n=7, controls n=8) Wistar rats were perfused in the Langendorff mode. The coronary perfusion pressures were held constant at 65 mmHg for the 14-day group and 80 mmHg in the adult group. After a 30 minute equilibration period, hearts were subjected to 30 minute global ischaemia (37C) and 2 hours reperfusion. In the intervention group, hearts were perfused with 5nM isoprenaline for 3 min followed by 0.3µM adenosine for 5 min prior to the onset of global ischaemia. Cardiac function through the experiment until 2 hours of reperfusion was assessed by measuring left ventricular developed pressure using a pressure transducer through a latex balloon inserted in the left ventricle and calculating the rate-pressure product (RPP). Results Pre- and post- ischaemia function was compared for each animal using the paired t-test. Consistent with earlier work, consecutive treatment of adult heart with isoprenaline and adenosine (Iso/Ade) was associated with marked and significant (p=0.03) improvement in percentage recovery in RPP after 2 hr reperfusion (20% recovery in controls, 45% in the intervention group). In contrast, the treatment did not improve recovery of RPP in postnatal heart (p=0.76; controls had a 25% recovery and interventions had a 26% recovery). Conclusion This work shows that the strong cardioprotective efficacy of Iso/Ade treatment is only seen in adult but not in postnatal heart. This difference is likely to be due to developmental changes in Isoprenaline-induced signalling pathways through cAMP and downstream mediators. Our observations highlight the need for further work regarding the fundamental cell signalling differences in the developing myocardium to develop effective cardioprotective interventions.