- unstable angina, preoperative arrhythmia, reduced ventricular function (ejection fraction < 40%), more than mild degree valvular heart disease, preoperative use of vasopressors or mechanical assist devices, intra-cardiac shunt, pulmonary artery hypertension, severe peripheral vascular obstructive disease, or esophageal pathology precluding the use of transesophageal echocardiography (TEE)