We examined the long-term effectiveness of a group-based psychological intervention (“MoVo-LISA”) to promote physical activity in patients with coronary heart disease. In this randomized controlled trial, N = 202 inactive patients with coronary heart disease were assigned to the control group (n = 102; treatment as usual) or the intervention group (n = 100; treatment as usual plus MoVo-LISA). Physical activity was assessed at baseline, 6 weeks (post-treatment), 6 months, and 12 months after discharge. ANCOVA for repeated measures revealed a significant interaction effect [p < .001; η p 2 = .214] indicating a large effect [d = 1.03] of the intervention on behavior change post-treatment. At 12-month follow-up, the level of physical activity in the intervention group was still 94 min per week higher than in the control group (p < .001; d = 0.57). Results of this RCT indicate that the MoVo-LISA intervention substantially improves the level of physical activity among initially inactive patients with coronary heart disease up to 1 year after the intervention.