Integrating the implicit-affect-primes-effort model (Gendolla, 2012, 2015) with the principles of motivational intensity theory (Brehm & Self, 1989) we investigated if the effort mobilization deficit observed in participants exposed to fear primes (vs. anger primes) in a difficult short-term memory task could be compensated by high monetary incentive. Effort was operationalized as cardiac response. We expected that fear primes should lead to the strongest cardiac pre-ejection period (PEP) reactivity when incentive was high (high subjective demand and high justified effort) and to the weakest response when incentive was low (high subjective demand but only low justified effort). PEP reactivity in the anger-prime conditions should fall in between (moderate subjective demand). We obtained the predicted pattern on responses of PEP and systolic blood pressure. The present findings show for the first time that the effort mobilization deficit of participants exposed to fear primes in a difficult cognitive task could be compensated by a high incentive.