OBJECTIVES: Detecting reduced left ventricular ejection fraction (LVEF) by an emergency physician (EP) is an important skill. The subjective ultrasound assessment of LVEF by EPs correlates with comprehensive echocardiogram (CE) results. Mitral annular plane systolic excursion (MAPSE) is an ultrasound measure of vertical movement of the mitral annulus, which correlates to LVEF in the cardiology literature, but has not been studied when measured by an EP. Our objective is to determine whether EP measured MAPSE can accurately predict LVEF <50% on CE. METHODS: This is a prospective observational single center study using a convenience sample to evaluate the use of a focused cardiac ultrasound (FOCUS) for patients with possible decompensated heart failure. The FOCUS included standard cardiac views to estimate LVEF, MAPSE, and E-point septal separation (EPSS). Abnormal MAPSE was defined as <8 mm and abnormal EPSS as >10 mm. The primary outcome assessed was the ability of an abnormal MAPSE to predict an LVEF <50% on CE. MAPSE also was compared to EP estimated LVEF and EPSS. Inter-rater reliability was determined by two investigators performing independent blinded review. RESULTS: We enrolled 61 subjects, 24 (39%) had an LVEF <50% on a CE. MAPSE <8 mm had a 42% sensitivity (95% CI 22-63), 89% specificity (95% CI 75-97), and accuracy of 71% for detecting LVEF <50%. MAPSE demonstrated lower sensitivity than EPSS (79% sensitivity [95% CI 58-93], and 76% specificity [95% CI 59-88]) and higher specificity than estimated LVEF (100% sensitivity [95% CI 86-100], 59% specificity [95% CI 42-75]). PPV and NPV for MAPSE was 71% (95% CI 47-88) and 70% (95% CI 62-77) respectively. The ROC for MAPSE <8 mm is 0.79 (95% CI 0.68-0.9). MAPSE measurement interrater reliability was 96%. CONCLUSIONS: In this exploratory study evaluating MAPSE measurements by EPs, we found the measurement was easy to perform with excellent agreement across users with minimal training. A MAPSE value <8 mm had moderate predictive value for LVEF <50% on CE and was more specific for reduced LVEF than qualitative assessment. MAPSE had high specificity for LVEF <50%. Further studies are needed to validate these results on a larger scale.