The Sarcoplasmic Recticulum (SR) plays a vital role in the activity of the sinoatrial node (SAN). Alterations in the expression and/or function of the proteins involved in SR calcium homeostasis with age could affect pacemaking and predispose to arrhythmias. During ageing there is a decline in response to stress partially due to a diminished response to adrenergic stimuli. Our hypothesis was that these age-associated problems may, at least in part, be explained by changes in SR function. Male Wistar rats at the ages of 6 months (young), 12 months (adult) and 24 months (old) (n=5 per group) were sacrificed by anaesthetic overdose via intraperitoneal injection. The SAN region of the heart was removed and intrinsic pacemaker activity recorded in bicarbonate-buffered saline at 37°C, under control conditions and in the presence of 3μM cyclopiazonic acid (CPA) to inhibit the sarcoendoplasmic reticulum ATPase pump (SERCA2a). Incrementing concentrations of isoprenaline (1nm, 10nm, 100nm and 1µm) assessed adrenergic response in the presence and absence of CPA. Western blot and immunocytochemistry measured expression of SERCA2a, phospholamban (PLB) and ryanodine receptors (RYR2). Data are mean±SEM percentages relative to the average young control values, compared by ANOVA with Holm-Sidak post-hoc tests (P<0.05). Isoprenaline (Iso) significantly increased the heart rate (young 100±3.3% vs. 139±4.9% in 1µm Iso: old 78±4.9% vs. 135±7.2% in 1µm Iso; p<0.05). The EC50 for Iso was significantly greater in old animals (24±3nM) than young (10±2nM). CPA caused significant pacemaker slowing (in the young reduction of 49±9bpm), but had a lower effect in the old (25±4bpm; p<0.05). In CPA there was no longer a difference in the EC50 for Iso between ages (mean 18±4nM). An age-associated decrease in conduction velocity was observed with age (young 100±2.2%; old 83±1.8%; p<0.05), however CPA had no affect on conduction at any age. Whereas Iso significantly increased conduction (Iso 1µm young 207±9% vs. old 122±1.1%; p<0.05). Young animals showed increased conduction velocity in low dose Iso, while only the maximum dose resulted in a significant increase in conduction within the old age group. SAN protein expression of SERCA2a, PLB and RYR2 was decreased in the old compared with the young (SERCA2a young 100±10.7% vs. old 60±10.4%; P<0.05: PLB young 100±10.8% vs. old 64±10.7%; P<0.05: RYR2 young 100±10.2% vs. old 68±15.3%; P<0.05). Similar decreases in expression of SERCA2a, PLB and RYR2 were observed in the right atria. In conclusion the expression of SR calcium handling proteins within the SAN exhibit an age-associated decline coupled with an attenuated response to adrenergic stimulation in the old animal.