This experiment investigated the combined effect of implicit affect and monetary success incentive on effort-related cardiac response in a 2 (Affect Prime: anger vs. sadness) × 2 (Incentive: low vs. high) between-person design. Sixty-two participants were exposed to affect primes during an objectively difficult short-term memory task. As predicted, by our theorizing about affect primes' systematic impact on subjectively experienced task demand and corresponding effort mobilization, sadness primes led to a weak cardiac pre-ejection period (PEP) response when incentive was low (disengagement), but to a very strong PEP response when incentive was high (high effort). PEP responses were moderate in the angerprime conditions (low effort). HR responses largely corresponded to those of PEP. The results demonstrate for the first time that high incentive can compensate the effort mobilization deficit of individuals who process sadness primes during a difficult task.