Abstract Background: Ischemic heart failure is a chronic and degenerative disease with high morbidity and mortality in the world. Coronary artery bypass grafting is indicated as elective treatment and may cause a catabolic state that depletes energy reserves. Data on body composition evaluation in the postoperative period of major cardiac surgery are limited. Objective: To evaluate the influence of elective coronary artery bypass grafting on body composition on the seventh postoperative day of patients with ischemic heart failure. Methods: A cross-sectional study was carried out in which eighteen volunteers with New York Heart Association Class II and III heart failure underwent coronary artery bypass grafting. The energy and protein reserves of the participants were evaluated by anthropometry in the preoperative and on the seventh postoperative day. Paired t-Test or Mann-Whitney test was used if applicable. A significance level was considered at p value < 0.05. Results: A significant loss of muscle mass was observed through the reduction of arm muscle circumference after surgery (4.2%, p 0.007). Major surgery causes hypermetabolic state and systemic inflammatory stimulus, due to the release of hormones and cytokines that may justify the observed loss of muscle mass. Conclusion: Coronary artery bypass grafting had an impact on muscle mass reduction seven days after surgery in patients with ischemic heart failure.