Objective: In heart failure, little information is available as to the Ca²⁺ release function of sarcoplasmic reticulum (SR), which plays a major role in cardiac contractile function. Here, we assessed the rapid kinetics of drug-induced Ca²⁺ release from cardiac SR in combination with a measurement of ryanodine binding in heart failure. Methods: The SR vesicles were isolated from dog left ventricular (LV) muscles (normal (N), n=10; pacing induced heart failure (HF), n=10). The time course of SR Ca²⁺ release was continuously monitored by a stopped-flow apparatus using arsenazo^III as a Ca²⁺ indicator, and Ca²⁺ uptake and [³H]ryanodine binding assays were done using a filtration method. Results: The amount of Ca²⁺ uptake was reduced in HF to 55% of N (P<0.05). Even the more marked and earlier appeared decrease was seen in the rate constant and the initial rate of polylysine (PL; a specific release trigger)-induced Ca²⁺ release (P<0.05). However, the PL concentration dependency of the initial rate shifted towards lower concentrations of PL in HF than in N ([PL] at half maximum stimulation=0.13 vs. 0.35 μM). The [³H]ryanodine binding assay revealed a lower B_max (pmol/mg) in HF than in N (0.91±0.19 vs. 2.64±0.59, P<0.05), but no difference in K_d (nM) (0.95±0.29 vs. 0.90±0.11, P=n.s.). The [PL] dependency on the enhancement of [³H]ryanodine binding again showed a shift towards lower [PL] in HF than in N. Conclusions: In pacing-induced heart failure, the Ca²⁺ releasing function of SR is disturbed, which may result in an intra-cellular Ca²⁺ transient that was slowed down.