OBJECTIVE To compare the accuracy of cardiovascular magnetic resonance (CMR) imaging methods for measuring left ventricular ejection fraction with multiple-gated acquisition (MUGA). CMR imaging methods included in-line tracking, in-line automated tracking with manual adjustment (a semiautomatic technique), and manual drawing techniques. METHODS Thirty patients were recruited for left ventricular ejection fraction (LVEF) assessment. The LVEF was measured by CMR imaging using in-line automated tracking, the semiautomatic technique, and manual contouring and segmentation. These methods were then followed by a MUGA scan. Results of all 4 methods were compared for LVEF percentage and measuring time. Repeated analysis of variance testing was used to determine any significant difference between the means of measuring the LVEF. A P value of less than .05 was considered statistically significant. RESULTS The mean LVEF measured by CMR imaging using in-line automated tracking, a semiautomatic technique, and manual drawing were 52.9% (standard deviation [SD] 8.5), 62.3% (SD 8.1), and 62.2% (SD 7.8), respectively. The mean LVEF with the MUGA scan was 64.4% (SD 8.4). The MUGA scan, semiautomatic technique, and manual measurement using CMR imaging were statistically significantly different from the CMR imaging using in-line automated tracking for LVEF calculation (all P values < .01). CONCLUSIONS Using in-line automated tracking, the end systolic volume was overestimated, which resulted in the underestimation of the LVEF. A therapeutic plan based on an inaccurate and low LVEF measurement could be dangerous because it might suggest a drug-related cardiotoxicity, and medication might be discontinued. CONCLUSIONS A semiautomated technique with manual adjustment of the cardiac contours and basal slice selection in CMR imaging is time saving and comparable with the MUGA scan for the accurate documentation of LVEF.