Aeitiology and pathophysiology of post-operative dyspnea is discussed. A strategy of arriving at a cause for post-operative dyspnea, with the help of parameters like the time of onset of dyspnea, associated symptoms like pain, use of narcotic analgesia, or anaphylactoid agents is given in a simplified manner. Even simple things like change of posture, could cause dyspnea. Correlation with other signs like tachycardia, fever, lung signs, increased jugular pulse, etc. is described. Investigation of dyspnea, with examination of pulse oximetry, arterial blood gases, ECG, X-ray chest, etc. is given.