Although atrial fibrillation (AF) is the most common arrhythmia and is associated with an increased risk of death, the mechanisms underlying its onset remain unclear. Remodelling of the atrial myocardium in heart disease is suggested to increase the risk of AF. Sympathetic stimulation (Coumel, 1996) and abnormal Ca2+ handling (Dobrev & Nattel, 2008) are also thought to play key roles in the genesis of the arrhythmia. We have previously shown that elevated afterload in rats, produced by surgical banding of the ascending aorta, results in atrial remodelling and increased susceptibility to AF (James et al. 2009); the objective of the present study, therefore, was to investigate the effect of β-adrenoceptor stimulation on Ca2+ signalling in left atrial myocytes in this model of elevated afterload. A silk ligature was tied around the ascending aorta of anaesthetised (combination of Ketamine (90mg/kg body weight)and Xylazine(6 mg/kg body weight) given i.p.) male Wistar rats via thoracotomy (AoB); sham-operated controls were subject to the same operation without aortic banding. 20 weeks following surgery, left atrial myocytes were isolated by Langendorff perfusion of the excised heart with a collagenase-containing solution. Isolated cells were loaded with fluo-3, superfused with Tyrode’s solution (~22°C), stimulated via field electrodes and intracellular Ca2+ concentration monitored by laser scanning confocal microscopy. Data are reported as mean ± S.E.M and were compared by paired or unpaired t-test. In cells from both AoB and Sham rats, peak intracellular Ca2+ during the systolic transient was greater at the sub-sarcolemma than in the central region of the cells: In Sham cells under control conditions, the peak of the Ca2+ transient at the sub-sarcolemma was 2.25 ± 0.15 F/F0, reached in 25.1 ± 2.0 ms, but it was difficult to identify a Ca2+ transient in the centre of the cells (n=5). On superfusion with the β-adrenoceptor agonist isoprenaline (1 μM), the peak at the sub-sarcolemma increased to 3.36 ± 0.16 F/F0 (P<0.01, paired t-test), with a time-to-peak of 31.5 ± 2.7 ms, and a Ca2+ transient of 1.74 ± 0.11 F/F0 that reached a peak in 151 ± 30 ms became evident in the centre of the cells (n=5). In AoB cells, the control sub-sarcolemmal Ca2+ transient was not significantly different from Sham cells (2.25 ± 0.17 F/F0, 31.1 ± 5.1 ms, n=5) and it was also difficult to identify a Ca2+ transient in the centre of the cells. However, in the presence of isoprenaline, the Ca2+ transient peak at the sub-sarcolemma (3.89 ± 0.14 F/F0) and centre (2.33 ± 0.19 F/F0) were significantly greater than those in Sham cells (P<0.05 in both cases, unpaired t-tests). These data suggest increased sensitivity to β-adrenoceptor stimulation of the systolic Ca2+ transient in rat left atrial myocytes with elevated afterload.