Background: This study aims to analyse whether in acute heart failure (AHF) with iron deficiency (ID), the administration of ferric carboxymaltose (FCM) produces a greater benefit in renal dysfunction. Methods: A total of 812 consecutive patients admitted for AHF and ID were studied. Untreated (n:272) and treated (n:540) patients were compared. The six-month prevalence of a combined event (readmission for HF, all-cause death, and emergency department visit for decompensation) was analysed. Three grades of renal dysfunction (KDIGO) were compared, Group 1 (grades 1 and 2), Group 2 (grades 3a and 3b), and Group 3 (grades 4 and 5). Results: There were differences in sex distribution (untreated group: males 39.7% vs. treated group: males 51.9%; p < 0.001). Sex-adjusted combined event analysis showed a greater benefit in Group 1 (OR: 0.31, 95% CI:0.19–0.5; p < 0.001) and Group 2 (OR: 0.23, 95% CI:0.14–0.38; p < 0.001), but not in Group 3 (OR: 0.51, 95% CI:0.17–0.55; p: 0.237). Conclusions: The administration of FCM in patients with AHF and ID reduces the combined event analysed. The benefit is greater when renal dysfunction is present, except in very advanced degrees where no significant benefit is obtained.