Aims Nuss procedure is an established and well approved minimally invasive technique for the correction of pectus excavatum. Hereby an individually curved steel bar is inserted to stabilize the thorax. This study aimed to describe ECG changes associated with this procedure. Methods and results Electrocardiographs of 65 patients who underwent Nuss procedure in our Hospital were evaluated before and after bar implantation as well as after bar removal. In the Goldberger leads, there was a consistent reduction in the QRS amplitude in lead I. In the Wilson leads, the most prominent change was a reduction in the QRS amplitude and a novel r' wave forming a slightly elevated J-point in the left lateral leads. Additionally, we noticed the loss of the former small and physiological q wave in the same leads, typical for an incomplete left bundle branch block (ILBBB). These changes resolved after bar removal. Conclusion We describe the common finding of a reversible incomplete ILBBB after Nuss surgery. The reason for these ECG changes remain unclear. Since cardiac ischaemia, damage, or perioperative irritation of the pericardium is improbable and the alteration of the anatomic thoracic situation remains after bar explantation, we suspect an artefact through alteration of the electric field by the steel bar. Practitioners dealing with patients after Nuss procedure should be aware of this most probably harmless finding.