Cytokines including tumour necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) are known to mediate systolic and diastolic myocardial dysfunction in sepsis. To provide a cellular basis we previously measured the effects of TNF-α on rat cardiac myocytes. Only changes to systolic function were observed [1]. In the present, more detailed study we separately measured the effects of 50 ng/ml TNF-α and IL-1β on intracellular Ca handling and contractility in sheep cardiac myocytes. Our aim was to provide further insight into the cellular basis of cytokine mediated myocardial dysfunction while using a translationally more relevant large mammal model. All procedures used accord with the Animals (Scientific Procedures) Act, UK, 1986 and Directive 2010/63/EU of the European Parliament. Ventricular myocytes were isolated from 18 month sheep, loaded with the Ca indicator Fura-2 then field stimulated at 0.5 Hz. Ca and contractility dynamics were measured by epi-fluorescent photometry and video sarcomere detection respectively. 50 ng/ml TNF-α and IL-1β reduced SR Ca content by 27 % and 41 % respectively, accounting for a 17 % and 24 % reduction each in the amplitude of systolic Ca. With TNF-α, the reduction of systolic Ca was associated with a 20 % reduction in sarcomere shortening, however IL-1β increased sarcomere shortening. The rate constant of systolic Ca decay was unaffected by both TNF-α and IL-1β. In response to both TNF-α and IL-1β the onset of systolic Ca decrease was rapid (<10 s), however, in 71 % of TNF-α treated cells and 52 % IL-1β treated cells, this was preceded by an immediate increase (58 and 52 % respectively) in systolic Ca, lasting for only 1-3 beats. TNF-α decreased diastolic Ca by 4 %, which was unchanged by IL-1β whilst diastolic sarcomere length was decreased by both cytokines. Though both cytokines reduced SR thence systolic Ca, only with TNF-α did this translate to reduced cell contractility. Given contractility was enhanced by IL-1β, and the fact that resting sarcomere length was decreased despite no increase in diastolic Ca suggest both cytokines may increase myofilament sensitivity. The mechanism by which SR Ca content is reduced remains unclear. Whilst SERCA impairment does not appear to play a role, the initial and short-lived increase of systolic Ca may suggest a role for ryanodine receptor potentiation [2]; a phenomenon we are currently investigating. While the changes to cell function produced by both cytokines can account for certain aspects of myocardial depression in sepsis, their individual contribution to the clinical phenotype may be more complex than previously thought. It is interesting that changes to diastolic function were only observed in sheep, highlighting the need to consider translationally important species dependent effects.