The atria are the site of the most common arrhythmia observed in clinical practice, atrial fibrillation (AF). It is hypothesized that abnormal calcium (Ca) handling in the atrial myocardium is involved in the pathogenesis of AF. As AF is strongly characterised by abnormalities in rate and rhythm, changes in these are frequently used as experimental manoeuvres to evaluate the behaviour, or to disclose abnormalities of Ca kinetics on excitation-contraction-coupling (1). Accordingly, post-rest-potentiation (PRP) allows indirect evaluation of sarcoplasmic reticulum (SR) function (2,3). PRP is a result of Ca accumulation in the SR during a pause, and an increased fractional release (FR) upon resumption of stimulation (3,4). Previous data focus on the length of the rest period, and how this affects PRP. In this study I aim to investigate the role stimulation frequency plays on PRP in sheep atrial myocytes. Atrial myocytes were isolated from the left auricle of healthy adult sheep, which were killed by an intravenously administered overdose of pentobarbitone (200mg/kg). Experimental protocols were carried out under perforated patch, voltage clamp conditions, at 37°C. Intracellular Ca was measured using fluo-5F at stimulation frequencies of 1, 3, and 5Hz. PRP measurements were taken after rest periods of 5 seconds. Ca changes are expressed as pseudo ratio (F/F0) measurements. An increase in stimulation frequency resulted in a rise in amplitude for the first Ca transient following a period of rest (2.77±0.41, 3.86±0.70, 3.96±0.38 at 1, 3, and 5Hz respectively, p<0.01, n=25). This indicates a positive relationship between PRP and stimulation frequency. Conversely at steady state an effect is observed, where Ca transient amplitude decreases with a rise in stimulation frequency (1.56±0.14, 1.14±0.07, 0.86±0.07, at 1, 3, and 5Hz respectively, p<0.01, n=39). There were no differences in peak L-type Ca current for the first PRP following rest, with changes in stimulation frequency. A rise in stimulation frequency results in an increase in the amplitude of the first Ca transient following a period of rest. In contrast, a negative Ca transient amplitude to frequency relationship is observed during periods of steady state. As there is no difference in peak L-type Ca current within the first transient post rest between each frequency, a greater amount of Ca released from the SR, as a result of increased SR Ca content may play a role, which could impact on the force generation upon the first activation following rest. However, as I have not directly measure SR Ca content after periods of rest further investigation is required. This positive relationship between PRP and stimulation frequency may play an important role in contraction under arrhythmic conditions.