Introduction: Respiratory assessment with spirometry in cardiothoracic surgeries is crucial for predicting postoperative respiratory complications. Its contraindication in patients with Unstable Angina (UA) or Acute Coronary Syndrome (ACS) lacks solid evidence. Spirometry could inform risk in urgent Coronary Artery Bypass Grafting (CABG). We aimed to compare the incidence of adverse events according to preoperative spirometry status. Methods: Retrospective cohort study including adults with UA or ACS scheduled for urgent CABG and assessed by pulmonology, grouped based on preoperative spirometry. The study spanned March 2010 to January 2017 at Hospital Italiano de Buenos Aires. Propensity score matching was performed to account for confounding by indication. Power analysis was performed to assess the risk of type 2 error. Results: 1192 clinical records were assessed, and 381 subjects were included. After 1:1 nearest-neighbor propensity score matching, 196 subjects per group were selected. Incidence density of events was 0.008 events/person/day and 0.021 events/person/day in the spirometry and control groups respectively. The majority of events were chest pain increase (77.8%). Incidence rate between groups was not statistically significant (0.42 CI95% 0.10-1.35, p=0.12).  Power analysis determined that using these parameters, this sample had a 6% type 2 error probability. Conclusions: The study suggests an acceptable safety margin for spirometry in a high-risk cardiac population. There was a low probability or lack of power, probably related to the large sample size. Future prospective studies may increase the robustness of our findings.