Introduction: Pectus excavatum (PEX) is a depression of the sternum which can physically constrict the heart and cause abnormal ECGs. The Nuss operation is a minimally invasive technique for PEX repair. Hypothesis: As right (RA) and left atria (LA) are compressed in PEX, axes of P, QRS, and T waves are abnormal and the Nuss operation normalizes them. We also took the Haller index (HI) into to account. Methods: 17 PEX patients (14 male, 12±6 years) underwent CT and ECG before and after the Nuss operation. Results: All Nuss operations were successful, and HI was significantly improved from 5.62±2.29 to 3.29±0.65 (P=0.0002). There were no significant differences before and after surgery for electrical axes of P waves (46±20 vs 65±55, P=0.20), and QRS waves (75±33 vs 76±23, P=0.72), but T waves were greater thereafter (22±27 vs 40±19, P=0.001). Correlation coefficients (CC) between the degree of axes of P, QRS and T waves, and HI before operation were -0.23, -0.06, and 0.11, respectively. These values after operation were -0.25, -0.06, and 0.19, respectively. As HI is an indirect indicator of heart compression, we evaluated the degree of RA and LA compression qualitatively as none, mild, and moderate/more. Of 17 patients, 5 had moderate/more compression of RA and/or LA by PEX (group 1); the remaining 12 did not show compression (group 2). Only P wave values were significantly smaller in group 1 than 2 before surgery, but these differences disappeared after surgery. In both groups, degree of axes of T waves was significantly greater after the operation. Conclusion: In patients with PEX, axes of T waves after the Nuss operation became significant greater than before the operation in patients with moderate or more compression of RA and/or LA by PEX. For P waves, this was smaller before the operation in those with compression but this was improved by the Nuss operation. P and T wave axes but not QRS could be therefore non-invasive indicators of Nuss operation success in addition to gross PEX appearance.