Background/Objectives: The ageing population has heightened interest in the prognostic role of geriatric conditions, notably frailty syndrome (FS) and cognitive impairment (CI). Evidence indicates a significant link between cardiovascular disease, FS, and CI. However, limited research has explored the impact of impaired functional and cognitive performance on outcomes in acute coronary syndrome (ACS) patients. This study aimed to evaluate the effect of coexisting FS and CI (FSxCI) on early and 6-month complications in older adults with ACS. Methods: This study included 196 ACS patients (119 men) aged 65 and over (mean = 74.7 years), with 90.8% undergoing invasive treatment (PCI in 81.6%, CABG in 9.2%). FS and CI were assessed on the third hospital day using the Tilburg Frailty Indicator (TFI) and Mini Mental State Examination (MMSE). Early (in-hospital) complications included major bleeding, ventricular arrhythmia (VT), conduction disturbances, cardiac arrest, stent thrombosis, acute heart failure (Killip–Kimball class III/IV), stroke, prolonged stay, and in-hospital death. Six-month follow-up recorded major adverse cardiovascular and cerebrovascular events (MACCEs). Results: Patients with FSxCI (n = 107, 54.6%) were older and had higher hypertension prevalence and lower nicotine dependence. FSxCI patients faced over twice the risk of prolonged hospital stays (OR 2.39; p = 0.01) and nearly three times the risk of early complications (OR 2.73; p < 0.001). At 6 months, FSxCI tripled the risk of MACCEs (OR 2.8; p = 0.007). Kaplan–Meier analysis confirmed a worse 6-month prognosis for FSxCI patients. Conclusions: Elderly patients with ACS and concomitant FSxCI had significantly higher rates of early (in-hospital) and 6-month complications. FSxCI was associated with a worse 6-month prognosis. This highlights its significance for clinical decision-making, as identifying FSxCI in ACS patients can help prioritize high-risk individuals for tailored interventions, optimize resource allocation, and improve outcomes.
