Introduction: Diabetes mellitus heightens the risk of myocardial infarction. Structured teaching programs on lifestyle modifications—diet, exercise, and stress management—are vital for reducing this risk and improving cardiovascular health in diabetic patients. Methodology: The study aims to evaluate diabetes mellitus patients' existing knowledge about lifestyle modifications for preventing myocardial infarction (MI), assess the impact of a structured teaching program on this knowledge, and analyze the relationship between posttest knowledge scores and various demographic variables. An evaluative research approach using a pre-experimental design with a single group pretest and posttest will be utilized. Data will be gathered through a structured questionnaire and the structured teaching program. The sample will consist of 60 participants, chosen through purposeful sampling, ensuring a focus on those relevant to the study's objectives. The research will be conducted at Chandra Hospital & Research Center and Axon Hospital in Lucknow. This approach aims to enhance diabetic patients' understanding of lifestyle changes crucial for MI prevention, ultimately contributing to improved health outcomes and effective preventive strategies. Result: In the study, pretest results showed that 55.5% of diabetes mellitus patients had insufficient knowledge about lifestyle modifications for preventing myocardial infarction (MI). Only 5% were well-informed, while 40% had moderate knowledge. The highest mean percentage (58.13%) was related to lifestyle changes for MI prevention, whereas overall concepts (47.6%), clinical aspects, diagnosis, and management of MI (43.75%), and MI etiology (43.66%) scored the lowest. The overall pretest knowledge score was 51.66% with a standard deviation of 3.9.Post-intervention, 25% of respondents had intermediate knowledge, 75% had appropriate knowledge, and no one had insufficient knowledge. The "t" value of 28.22, significant at the 0.01 level, confirmed a significant improvement in knowledge. Additionally, the chi-square analysis at the 0.05 level showed a significant relationship between posttest knowledge scores and demographic variables like income, education, and religion, but not with age, gender, or lifestyle factors. Conclusion: This highlights the effectiveness of the STP in enhancing knowledge and its relevance to specific demographic factors.