INTRODUCTION: In cardiac muscle the amplitude and duration of the systolic calcium (Ca) transient and thence contraction are modulated by the release and re-uptake of Ca from the sarcoplasmic reticulum (SR). In heart failure there is a decrease in both the amplitude and rate constant of decay of the Ca transient. These result in part from decreased sarco/endoplasmic reticulum ATPase activity but also due to increased leak through the SR Ca release channel (Ryanodine Receptor, RyR). The objective of this study was to determine whether the reduction in the amplitude and rate constant of decay of the systolic Ca transient caused by severe SR Ca leak can be corrected by decreasing the opening of the RyR. METHODS: Experiments were performed on rat ventricular myocytes, voltage-clamped using the perforated patch clamp technique and stimulated at 0.5 Hz with 100 ms duration depolarizing pulses from -40 mV to 0 mV. Cytosolic Ca concentration was measured using the fluorescent indicator Fluo-3 AM. Data are described as mean ±SEM. Tests for statistical significance were performed using one way ANOVA. RESULTS: The application of 2 mM caffeine to increase leak through the RyR decreased the amplitude of the Ca transient from 769 ± 160 nM to 158 ± 28 nM (n=12, p =0.001). This was accompanied by a decrease in the rate constant of decay of the systolic Ca transient from 13.5±1.6 second-1 to 6.8 ± 0.65 second-1(p=0.001). We next investigated the effects of decreasing RyR leak by adding 100 µM tetracaine (in the continued presence of caffeine) to decrease RyR opening. This resulted in an initial decrease in the amplitude of the Ca transient, due to decreased RyR opening. This was, however, followed by an increase of both the amplitude and rate constant to levels greater than those observed in caffeine alone (334±68.6 nM;p=0.026 and 10.8± 1.2 second-1 ;p=0.02 CONCLUSIONS: In our experiments, inhibition of RyR with 100µM tetracaine partially restores the changes in Ca transient amplitude and rate of decay produced by severe SR Ca leak induced with 2mM caffeine. These results suggest that inhibition of RyR and reduction of SR Ca leak could represent a viable treatment strategy to improve contractility and relaxation in patients with heart failure.