This experiment investigated the moderating effect of masked anger versus sadness primes on objective task difficulty's impact on effort-related cardiovascular response. Cardiovascular measures (ICG and blood pressure) were assessed during a habituation period and an easy versus difficult short-term memory task during which participants were exposed to masked emotional facial expressions. As expected, sadness primes led to stronger cardiac preejection period (PEP) responses than anger primes when the task was easy. When the task was difficult, we observed the reversed pattern. Here, anger primes led to stronger PEP reactivity than sadness primes. Heart rate responses described the corresponding pattern. The results demonstrate that masked anger and sadness primes have different effects on cardiac response in easy and difficult tasks. The effect of anger primes resembles the facilitating effect of happiness primes observed in previous studies.