- History of right to left, bi-directional or transient right to left cardiac shunts, worsening or clinically unstable congestive heart failure, acute myocardial infarction or acute coronary syndromes serious ventricular arrhythmias or high risk for arrhythmias due to prolongation of the QT interval, respiratory failure as manifested by signs or symptoms of carbon dioxide retention or hypoxemia or severe emphysema, pulmonary emboli or other conditions that causes pulmonary hypertension due to compromised pulmonary arterial vasculature