In patients with severe aortic stenosis (AS), the presence of pulmonary hypertension (PH) has been linked to a poor prognosis. We aimed to assess the main determinants of PH in patients with severe AS and preserved left ventricular ejection fraction (LVEF). We prospectively enrolled 108 consecutive patients with isolated severe AS (indexed aortic valve area <0.6 cm²/m²) and LVEF >50%, in sinus rhythm. Left atrial (LA) function was assessed using longitudinal deformation parameters (by speckle tracking echocardiography). PH (defined as systolic pulmonary artery pressure >40 mmHg) was present in 20 patients. Patients with severe AS and PH were older (p = 0.05), had higher BNP values (p = 0.05) and a greater degree of LV diastolic dysfunction: higher E/e′ and E/A ratios and lower EDT values (p < 0.03 for all) compared to patients without PH. There were no differences between groups regarding AS severity and LV systolic function parameters. Patients with PH had a more impaired LA function: lower septal and lateral late diastolic peak velocity a′ (p < 0.001 and p = 0.04 respectively) and lower LA peak longitudinal strain and strain rate parameters (p ≤ 0.005 for all). In multivariable analysis, LA late diastolic longitudinal strain rate was the only independent correlate of PH in our patients (p = 0.04). Patients with isolated severe AS, preserved LVEF and PH had larger LA volumes, a more impaired LA function, and higher LV filling pressures compared to those without PH. LA booster pump function, reflected by late diastolic longitudinal strain rate, emerged as an independent correlate of PH in these patients.