Intercostal branches of the internal mammary artery (IMA) are usually tied off during IMA-bypass surgery. Some side-branches may be missed, however, due to anatomical variants or during minimal invasive procedures with limitation of the surgeon's ability to ligate proximal branches. There are a number of reports in the literature describing interventional closure of side-branches using Gianturco coils. Following embolization or malposition, however, these coils may be extremely difficult to retrieve from coronary arteries. We report about interventional embolization of a IMA side-branch with detachable micro-coils in a patient with symptomatic coronary steal. Detachable coils are safer than Gianturco coils and are an effective method to abolish symptomatic coronary steal due to unligated intercostal branches of the IMA graft.