OBJECTIVE To identify echocardiographic factors that correlate with pulmonary hypertension (PH) in adults with ostium secundum atrial septal defect (ASD). METHODS Between November 2009 and November 2013, 92 adults with ASD were studied. All had clinical history and transthoracic echocardiogram. RESULTS Thirty-nine percent of patients had severe PH defined as systolic pulmonary artery pressure (sPAP) of 70 mm Hg or more. The size of ASD (31.84±8.21 mm) and a right-sided tricuspid inflow E-wave to tissue Doppler e'-wave ratio >6.2 correlated with severe PH with AUC of 0.704 (CI 95%=0.59 to 0.818, P<.001) and 0.65 (CI 95%=0.531 to 0.773, P<.014), respectively. Multivariate logistic regression showed that sPAP >70 mm Hg was the variable that most precisely correlated with right ventricular (RV) dysfunction as evidenced by TAPSE <17 mm and RV fractional shortening area (RVFSA) <35%. Left ventricular (LV) diastolic function was also significantly reduced in the group with severe PH with mitral inflow E/A ratio of 0.73±0.23 vs 1.13±0.42 in the group without severe PH (sPAP <70 mm Hg, (P=.001). The pulmonary (Qp) to systemic (Qs) cardiac output ratio (3.09±1.12) and right-sided tissue Doppler S <9.5 cm/s most accurately predicted a Tei index >0.55. CONCLUSIONS Larger size of ASD using the QP/QS ratio and increased right-sided tricuspid E/e' ratio correlated with severe PH with a sPAP of 70 mm Hg or more. Patients with severe PH had more severe RV dysfunction as evaluated by TAPSE and RVFSA in comparison to those with PH <70 mm Hg. LV diastolic function was also reduced in the severe PH group.