Experiments were conducted in 10 isolated rabbit hearts at 25°C to test the hypothesis that vibration-induced depression of myocardial contractile function was the result of increased cross-bridge breakage. Small-amplitude sinusoidal changes in left ventricular volume were administered at frequencies of 25, 50, and 76.9 Hz. The resulting pressure response consisted of a depressive response [P_d(t), a sustained decrease in pressure that was not at the perturbation frequency] and an in-frequency response [P_f(t), that part at the perturbation frequency]. P_d(t) represented the effects of contractile depression. A cross-bridge model was applied to P_f(t) to estimate cross-bridge cycling parameters. Responses were obtained during Ca²⁺ activation and during Sr²⁺ activation when the time course of pressure development was slowed by a factor of 3. P_d(t) was strongly affected by whether the responses were activated by Ca²⁺ or by Sr²⁺. In the Sr²⁺-activated state, P_d(t) declined while pressure was rising and relaxation rate decreased. During Ca²⁺ and Sr²⁺ activation, velocity of myofilament sliding was insignificant as a predictor of P_d(t) or, when it was significant, participated by reducing P_d(t) rather than contributing to its magnitude. Furthermore, there was no difference in cross-bridge cycling rate constants when the Ca²⁺-activated state was compared with the Sr²⁺-activated state. An increase in cross-bridge detachment rate constant with volume-induced change in cross-bridge distortion could not be detected. Finally, processes responsible for P_d(t) occurred at slower frequencies than those of cross-bridge detachment. Collectively, these results argue against a cross-bridge detachment basis for vibration-induced myocardial depression.