Objectives: Based on the Implicit-Affect-Primes-Affect (IAPE) model (Gendolla, 2012, 2015), we investigated the effect of affect primes' visibility on effort-related cardiac response. Methods: Participants worked on a cognitive “parity task” with integrated pictures of sad vs. angry faces that were briefly flashed (25 ms) vs. clearly visible (780 ms). We recorded cardiac pre-ejection period (PEP) to assess effort mobilization. Results: As expected, PEP reactivity in the sadness-prime condition was stronger than in the anger-prime condition when the primes were briefly flashed, while the opposite pattern occurred when the affect primes were clearly visible. However, these effects only occurred for men, but not for women, as indicated by a significant prime x prime visibility x gender interaction. Conclusions: These findings provide new evidence for the role of prime visibility as a moderator of automatic effort mobilization—and suggest that this moderator effect applies especially to men.