PFT derangements are seen in all grades of severity of MS and correlate well with the functional class, though no significant linear correlation with grades of severity of stenosis or pulmonary hypertension. Even the early or mild derangements in pulmonary function such as small airway obstruction in the less severe cases of normal or mild PH can be detected by simple and inexpensive methods when the conventional parameters are normal. The supplementary data from baseline arterial blood gas analysis is informative and relevant. This reclassified pulmonary function status might be prognostically predictive.