This report presents three patients with severe pulmonary hypertension secondary to atrial septal defect associated with thrombus and spontaneous echo contrast within the pulmonary artery diagnosed by transthoracic and transoesophageal echocardiography. Clinical and echocardiographic features seem to suggest local thrombus formation within the pulmonary arteries as a direct consequence of pulmonary hypertension rather than venous thromboembolism.