Aim. Left ventricular (LV) ejection fraction (EF) and perfusion defect size (PDS) provide independent and incremental prognostic information in patients with coronary artery disease (CAD). The purpose of this study was to examine the correlation between EF and PDS. Methods. LVEF and PDS were measured in 96 consecutive patients with CAD and abnormal perfusion scan using well-validated automated programs. The PDS was expressed as % of LV myocardium as total (reversible plus fixed), fixed or reversible. Results. The EF was 49±15% (range 17-84), the total PDS was 29±15% (2-77) and the fixed PDS was 20±13% (2-58). The end-diastolic volume (EDV) was 131±59 mL (29-342) and end-systolic volume (ESV) was 72±51 mL (4-283). There were moderate but significant correlations between EF and total PDS (r=- 0.46, P<0.0001) and fixed PDS (r=-0.45, P<0.0001) but not with reversible PDS. In the subgroup analysis, the correlations were stronger in patients with history of prior coronary artery bypass grafting than without, and higher in men than women. The highest correlations were seen between EF and EDV in both men and women (r=-0.68 and -0.74 respectively, P<0.0001 each), and between EF and ESV (r =-0.80, P<0.0001). Conclusions. Although there is a statistically significant correlation between PDS and EF, the correlation is not strong. This observation provides supportive evidence of why PDS and EF provide incremental pro-gnostic information. It also supports the incremental prognostic merits of LV volume measurements.