Cardiac-sympathetic state predicts action restraint, gated by demonstrated agency

Abstract Withholding action until the appropriate moment is a core challenge of motivated behavior. Using beat-to-beat cardiac contractility during an incentivized reaching task, we show that cardiac-sympathetic outflow predicts action restraint. Under high-reward conditions that induce a speed–accuracy tradeoff, reduced contractility at the time of instruction preceded premature responses (false starts). Under high-loss-avoidance conditions, elevated pre-movement contractility predicted slower, more controlled initiation, but only among participants with above-median task success. These findings suggest cardiac-sympathetic engagement does not simply serve mobilization but flexibly supports context-appropriate action regulation, with recruitment for restraint gated by demonstrated agency.