The balance between Ca influx and efflux regulates intracellular Ca (Cai) in cardiac myocytes (1). The main Ca influx pathway, ICa, has recently been shown to be redistributed from t-tubules (TT) to surface sarcolemma (SS) in ventricular myocytes from failing hearts (2). However, whether the main Ca efflux pathway, Na-Ca exchange (NCX), is redistributed in heart failure is unknown. Animal procedures were performed in accordance with UK legislation and approved by the local Ethics Committee. Coronary artery ligation (CAL) and sham operations (Sham) were performed in adult male Wistar rats under surgical anaesthesia (ketamine 75 mg/kg, medetomidine 0.5 mg/kg ip) with appropriate analgesia (buprenorphine 0.05 mg/kg sc). 18 weeks after surgery hearts were excised under pentobarbitone anaesthesia (140 mg/kg ip) and left ventricular myocytes isolated by enzymatic digestion. NCX current (INCX) was measured at -80 mV during application of 10 mM caffeine (to release sarcoplasmic reticulum Ca), using whole-cell patch-clamp. Cai was measured simultaneously using fluo-4. Recordings were made in intact (Sham n=12, CAL n=8) and detubulated (DT; Sham n=11, CAL n=7) myocytes at room temperature. Data are presented as mean±SEM and analysed by 2-way ANOVA with Bonferroni post-test. The rate of decline of the caffeine-induced Cai transient (kCaff, a measure of sarcolemmal Ca efflux) in Sham cells was significantly slowed by DT (0.80±0.07 vs. 0.35±0.04 s-1, P<0.001). kCaff was slower in CAL than in Sham cells (0.41±0.05 s-1 P<0.05) but was unaffected by DT (0.48±0.03 s-1). Exposure to caffeine was repeated in the presence of 10 mM Ni (to inhibit NCX) and the rate of Ca removal via NCX calculated as the difference between the rate of removal in the absence and presence of Ni. In Sham cells, DT decreased the rate of Ca removal via NCX (kNCX, 0.65±0.06 vs. 0.26±0.04 s-1; p<0.001). kNCX in CAL cells was not statistically different from Sham (0.35±0.05 s-1), and was not altered by DT (0.35±0.03 s-1). INCX density at 400 nM Cai, during the descending phase of the caffeine-induced Ca transient, was not significantly different between intact Sham and CAL cells (-0.27±0.08 vs. -0.38±0.08 pA/pF). However, calculating TT INCX from the difference in INCX between intact and DT myocytes confirmed that INCX was located predominantly at the TT in Sham myocytes, as reported previously (3). However, INCX in CAL cells was ~53% lower at the TT and ~270% higher at the SS, compared with Sham cells. These data demonstrate that INCX is redistributed from TT to SS in the rat CAL model of heart failure. Changes in the localization of NCX function are likely to contribute to abnormalities in Ca homeostasis and susceptibility to triggered pro-arrhythmic events in heart failure.