Two experiments found that effort-related cardiovascular reactivity under ego-involvement follows the principles of motivational intensity theory. Experiment 1 manipulated ego-involvement and the difficulty of a memory task. Under high ego-involvement, cardiovascular reactivity during task performance increased with fixed task difficulty; an unfixed performance standard elicited the same high reactivity as a fixed high standard. Experiment 2 manipulated ego-involvement and administered a memory task with unfixed versus extremely high performance standards. High ego-involvement increased cardiovascular reactivity only when the performance standard was unfixed but not when success was obviously impossible. Both studies found associations between cardiovascular reactivity and achievement and controlled for emotional states. The findings clarify previous research and theorizing about ego-involvement and motivation.