We read with great interest the article on cardiac diastolic dysfunction in patients with pulmonary arterial hypertension by Tonelli et al1 published in CHEST (June 2012). We appreciate their original and interesting contribution, especially when there is limited knowledge on the topic. Echocardiography is the most commonly used method for studying diastolic dysfunction. However, we should keep in mind that current echocardiographic diastolic classification may not be suited to respiratory patients because in these patients the volume of the left atrium is decreased, as Tonelli et al1 and other authors2 have reported. In most patients with diastolic dysfunction, the dysfunction occurs when the left atrium is dilated, reflecting the cumulative effects of filling pressures over time. This dilatation is a key point in the diagnosis of diastolic dysfunction, even in mild (or grade I type) cases. In specific patents with a nondilated left atrium, caution should be exercised when diastolic classification is applied.