Background: The present study aimed to compare the effectiveness of Acceptance and Commitment Therapy (ACT) and GUIDED IMAGERY (GI) in the Emotional Regulation (ER) of cardiovascular patients referred to a cardiac rehabilitation department. Methods: This was an experimental study with a pre-test, post-test design and a 45-day followup. Using the purposive sampling method, 45 patients with cardiovascular diseases were selected among those who referred to the cardiac rehabilitation ward of Imam Reza Hospital, Mashhad City, Iran, from March to August 2017,the patients were then assigned into three groups. The intervention groups received ACT or GI programs. Also, the patients completed the Cognitive Emotion Regulation Questionnaire in three stages of pre-test, post-test, and follow-up. Results: The obtained data indicated a significant difference between the ACT and GI groups, concerning positive and negative ER. Also, the analysis of variance suggested the effectiveness of both interventions in the studied subjects (P<0. 001). Besides, the effectiveness of ACT was significantly greater than that of GI in increasing positive and negative ER among the studied patients. Conclusion: The present findings reveal that experiential avoidance—, as one of the main cores of psychological inflexibility in ACT—, is significantly and negatively correlated with adaptive ER strategies. One of the main goals of ACT is to reduce avoidance, thus, ACT can improve adaptive ER strategies. Accordingly, ACT is more effective than GI in increasing positive ER strategies in patients with cardiovascular diseases.