Objective: Our objective was to introduce a new index to evaluate left ventricular aneurysm by quantitative analysis of left ventricular apical geometry. Methods: A total of 116 selected subjects underwent magnetic resonance imaging, 28 healthy volunteers, 29 patients with dilated cardiomyopathy, and 59 patients with ischemic heart disease (26 with left ventricular aneurysm; 33 with no aneurysm). The apical conicity ratio was calculated as the ratio of left ventricular apical area over apical triangle. Results: Diastolic apical conicity ratio of patients with left ventricular aneurysm was 1.62 ± 0.20 and systolic apical conicity ratio was 1.78 ± 0.43. After left ventricular reconstruction, the diastolic apical conicity ratio decreased to 1.47 ± 0.23 and the systolic ratio to 1.51 ± 0.21, which came close to the normal level, whereas other global indices remained. In patients with dilated cardiomyopathy, sphericity index and eccentricity index increased significantly without changes in the apical conicity ratio. Among patients with ischemic heart disease, the apical conicity ratio of the group with left ventricular aneurysm was significantly higher than that of the group without an aneurysm when the other indices between the 2 groups showed no statistically difference. Receiver operating characteristic curves showed only apical conicity ratio had high power of discriminating left ventricular aneurysm from no aneurysm. Conclusions: The new index, apical conicity ratio, can be used to quantify the regional left ventricular deformation, especially in patients with left ventricular aneurysm resulting from myocardial infarction. © 2010 by The American Association for Thoracic Surgery.