Fluorescent and mechanical responses to a series of electrical impulses of papillary muscle bands of the rabbit right ventricle during glucose oxidation were investigated. The kinetics of fluorescent responses consists of two phases: the primary one--the fall, and secondary one--the rise of NADN fluorescence up to the initial level and higher (overshoot). The fluorescence change in the first phase and overshoot value increase in response to an increased mechanical load, as well as to an increased concentration of extracellular Ca++ or adrenaline injection. No fluorescent response is observed after cyanide injection. Monoiodacetate eliminates overshoot initiation. Prolonged stimulation under large mechanical loads is accompanied by the stationary level of fluorescence above the initial one. This effect is interpreted on the basis of mathematical models [1, 2], as a result of pyruvate level control of the rate of NADN production by the Krebs cycle.