Abstract Background Heart surgery is associated with an occurrence of pulmonary complications. The aim of this study was to determine whether pre-surgery respiratory physiotherapy reduces the incidence of post-surgery pulmonary complications. Methods Observational study of 263 patients submitted to off-pump coronary artery bypass grafting (CABG) surgery at the A Coruña University Hospital (Spain). 159 (60.5%) patients received preoperative physiotherapy. The fact that patients received preoperative physiotherapy or not was related to whether they were admitted to the cardiac surgery unit or to an alternative unit due to a lack of beds. A physiotherapist provided a daily session involving incentive spirometry, deep breathing exercises, coughing and early ambulation. A logistic regression analysis was carried out in order to identify variables associated with pulmonary complications. Results Both groups of patients (those that received physiotherapy and those that did not) were similar in age, sex, body mass index, creatinine, ejection fraction, number of affected vessels, O₂ basal saturation, prevalence of diabetes, dyslipidemia, exposure to tobacco, age at smoking initiation, number of cigarettes/day and number of years as a smoker. The most frequent postoperative complications were hypoventilation (90.7%), pleural effusion (47.5%) and atelectasis (24.7%). In the univariate analysis, prophylactic physiotherapy was associated with a lower incidence of atelectasis (17% compared to 36%, p = 0.01). After taking into account age, sex, ejection fraction and whether the patients received physiotherapy or not, we observed that receiving physiotherapy is the variable with an independent effect on predicting atelectasis. Conclusion Preoperative respiratory physiotherapy is related to a lower incidence of atelectasis.