Background/Objectives: Malnutrition has been associated with increased morbidity and mortality in elderly patients diagnosed with heart failure (HF). However, nutritional problems are underdiagnosed in these patients. This study aimed to analyse malnutrition prevalence in elderly HF patients and its impact on survival. Methods: We conducted a retrospective observational study including patients aged ≥85 years diagnosed with HF followed up by a specific HF unit between 2015 and 2023. All patients underwent a nutritional assessment at the start of follow-up. Demographic characteristics, comorbidities, functional, cognitive and frailty status, heart disease characteristics and laboratory data, as well as admissions, emergency department visits and survival, were collected. The sample was categorised according to nutritional status into normonutrition and impaired nutritional status, and differences were evaluated. Results: Of a total of 413 patients, 52.8% were female, and the mean age was 88.4 ± 2.9 years. A total of 25.4% were at risk of malnutrition and 2.2% malnourished. Dementia [OR = 3.99, 95%CI (2.32–6.86); p < 0.001], hip fracture [OR = 3.54, 95%CI (1.75–7.16); p < 0.001)], worse Barthel index score [OR = 5.44, 95%CI (3.15–9.38); p < 0.001), worse Pfeiffer test [OR = 5.45; 95%CI (3.29–9.04); p < 0.001), worse Frail index [OR = 6.19; 95%CI (2.45–15.61); p < 0.001] and higher Charlson index [OR = 1.95; 95%CI (1.21–3.15); p = 0.006] were associated with worse nutritional status. In addition, patients with poor nutritional status lived 16.69 months less (p < 0.001) than normonutrited patients. Conclusions: At least one in four elderly patients with HF under outpatient follow-up has an impaired nutritional status. This is associated with hip fracture and greater functional and cognitive decline. Patients who are malnourished or at risk of malnutrition survive less than those who are not malnourished.