Abstract Background/Introduction A low estimated glomerular filtration rate (eGFR) has been identified as a poor prognostic factor in patients with cardiovascular diseases (CVD). Since serum creatinine, which defines eGFR, is a metabolite of skeletal muscle, low skeletal muscle mass can result in reduced creatinine production and potentially overestimate renal function. This raises concerns about the reliability of eGFR as a prognostic indicator in patients with both CVD and sarcopenia. The impact of this relationship, however, remains uncertain. Purpose This study aimed to explore the association between eGFR and prognosis in patients with CVD, both with and without sarcopenia. Methods We included 2,444 CVD patients (mean age 69.0 ± 13.7 years) who had assessments of eGFR and sarcopenia at discharge. Sarcopenia was diagnosed according to the 2019 Asian Sarcopenia Working Group Diagnostic Criteria. Patients were categorized into sarcopenia and non-sarcopenia groups, each further divided into high eGFR (eGFR ≥60 mL/min/1.73 m²) and low eGFR (eGFR <60 mL/min/1.73 m²) subgroups. Kaplan-Meier curves, log-rank tests, and multivariate Cox regression analyses were employed to compare prognoses between these groups, adjusting for age, sex, BMI, left ventricular ejection fraction (LVEF), history of myocardial infarction (MI), acute coronary syndrome (ACS), heart failure (HF), hypertension (HT), dyslipidaemia (DL), diabetes mellitus (DM), and smoking history. The primary endpoint was a composite of all-cause mortality and rehospitalization. Results Median follow-up was 1.11 (interquartile range [IQR], 0.43–2.32) years for the non-sarcopenia group and 0.94 (IQR, 0.30–2.15) years for the sarcopenia group. Event rates were 24.2% in the non-sarcopenia group and 30.8% in the sarcopenia group. Both Kaplan-Meier and log-rank tests indicated that a low eGFR, regardless of sarcopenia status, was associated with a higher incidence of composite events (p < 0.001). Multivariate Cox regression analysis revealed a significant association between low eGFR and increased risk of composite events in both the non-sarcopenia [hazard ratio (HR): 1.55, 95% confidence interval (CI): 1.44–1.67; p < 0.001] and sarcopenia groups [HR: 1.36, 95% CI: 1.25–1.48; p < 0.001]. Conclusion Low eGFR is associated with poor prognosis in patients with CVD, irrespective of sarcopenia status.