Partial or complete recurrent lung collapse after cardiac surgery is one cause of failure to wean from ventilator support, and frequently leads to multiple reintubations and prolonging intensive care unit and hospital stays. A 79-year-old female underwent uneventful coronary artery bypass surgery and was extubated on the first postoperative day (POD). On POD 2, a routine portable chest X-ray (CXR) revealed complete opacification of the left hemithorax. The patient was readmitted to the Cardiovascular Intensive Care Unit (CVICU) and electively intubated, and bronchoscopy revealed a left mainstem bronchus mucous plug. The patient was extubated uneventfully the same day. A CXR on the next day revealed recurrent total collapse of the left lung, which this time was successfully treated non-invasively with intermittent CPAP mask, percussive therapy, and respiratory treatments using acetylcysteine solution. After several days, the left lung collapsed again, necessitating reintubation and repeat bronchoscopy. With Pulmonary medicine present, the patient was subsequently extubated so that bronchoscopy could be performed while the patient was breathing spontaneously. This examination revealed dynamic collapse of the left lower lobe bronchus. A sniff test was performed and revealed an immobile left hemi-diaphragm. The patient gradually became stronger, and as the airway edema subsided, she was able to be managed on the regular nursing floor with intermittent CPAP mask treatments and mucolytics. Although uncommon, one documented cause of failure to wean from mechanical ventilation is diaphragmatic dysfunction. This finding is often delayed because it requires a sniff test in an extubated patient to make the diagnosis.