Hey :) EF and functional SV/CO are different entities - can have low EF with an adequate forward SV (think the dilated cardiomyopathy population walking around in the community) or a high EF with a low SV (e.g. hypertrophic cardiomyopathy with a small LV end diastolic volume). The difference is potentially even more marked and dynamic in critical care. Very high EF in septic shock not necessarily good (increased risk of septic cardiomyopathy). Slightly low EF *might* be protective. High EF might also indicate another problem in shocked patient - e.g. acute severe MR (can be v difficult to see) or VSD. In other words - EF looks great, but all the flow is going backwards. Hence - contextualise EF with cardiac output measurements for full picture. Hope that helps.