Sub-threshold stimuli cannot initiate excitations in active media in the resting state, but surprisingly as we show in this paper, they can alter the time-evolution of spatially heterogeneous activity by modifying the recovery dynamics. This results in significant reduction of wave back velocity which may lead to spatial coherence, terminating all activity in the medium including spatiotemporal chaos. We analytically derive model-independent conditions for which such behavior can be observed. The phenomenon reported here may have possible implications for the termination of life-threatening cardiac arrhythmias (eg, fibrillation) by external electrical stimuli.