Prevailing social cognition models consider behavioural intentions as immediate precursors of actions. This view ignores the role of more proximal self-regulatory processes, such as action control. The latter emerges after an intention has been formed and is supposed to maintain the level of intentions over time and to translate them into action. Three facets of action control were examined in terms of their predictive power for changes in intentions and for physical exercise: (a) awareness of standards, (b) self-monitoring, and (c) self-regulatory effort. A parsimonious 6-item instrument was administered to 122 cardiac patients at six weekly measurement points in time following rehabilitation. A distinction was made between the level of action control and the degree of change in action control, applying a latent growth model. While awareness of standards remained stable, the other two facets exhibited a linear change over the six-week period. Level and change were distinct predictors of physical exercise and changes in intentions. These findings emphasize the importance of self-regulatory mechanisms in the first weeks of trying to overcome a sedentary lifestyle. Action control may be a promising construct to narrow the intention-behaviour gap.