Heart failure (HF) is a major cause of mortality and morbidity in most of the world. In 2012, 2.4% people in the United States had HF. 1 HF can be classified into either HF with reduced ejection fraction (HFrEF) or HF with preserved ejection fraction (HFpEF). Treatment choice for HF is guided predominantly by symptoms and left ventricular ejection fraction (LVEF). 1 LVEF is one of the most important measurements used to evaluate HF patients. Based on the current 2013 American College of Cardiology/American Heart Association (ACC/AHA) guidelines on management of HF, measurement of LVEF is a class I recommendation for evaluating patients with HF. 1 This measurement clearly defines (1) prognosis, (2) mode of treatment with devices (implantable cardiac defibrillators [ICDs] and cardiac resynchronization therapy), and (3) types of medical therapy, such as use of neurohormonal therapy 1 and titration of chemotherapy. 2,3 Currently, LVEF can be measured by an echocardiogram (ECHO), single-photon emission computed tomography (SPECT), contrast-enhanced left ventriculogram, cardiac computed tomography (CCT), and cardiac magnetic resonance imaging (CMR). 4,5 None of these techniques are without problems, and all have some limitations. Up to 10% variability may be found in the LVEF by ECHO in the same examination. 2,3,6 The most accurate test is felt to be CMR and is used in most studies as the "gold standard" to evaluate the accuracy of LVEF measured by other techniques. 4,5 However, the expense, availability, and the inability to use CMR in patients who have pacemakers or artificial valves limit its use. Many studies have reviewed the correlation of LVEF determined by ECHO and SPECT compared to CMR as the gold standard. Although LVEF by ECHO is the standard guideline-approved technique 1,2 to measure LVEF in most HF patients, SPECT is an accepted modality to determine LVEF. 1,7,8 Both ECHO and SPECT have their limitations. 7,9