Aim: A cross-sectional observational study of serum parathyroid hormone levels and its relation with severity and duration of heart failure. Material and methods: The present study included a cohort of 80 consecutive outpatients diagnosed with systolic heart failure. The echocardiogram revealed that the left ventricular ejection fraction (LVEF) was less than 40% in all of the patients. Blood samples were obtained in order to measure intact parathyroid hormone (PTH) and brain natriuretic peptide (BNP). Serum intact parathyroid hormone (PTH) levels were collected at an outpatient clinic utilizing an Immulite intact PTH assay manufactured by Diagnostics Product Corporation in 2000, located in Los Angeles, California. The assay's established normal range was determined to be between 10 and 65 pg/ml. The patients were categorized into four distinct groups according to the New York Heart Association (NYHA) functional class. Results: The mean left ventricular ejection fraction (LVEF) was found to be 26.85±7.78, while the mean parathyroid hormone (PTH) level was measured to be 102.55±13.55 pg/ml. Sixteen patients (20%) exhibited advanced heart failure, as determined by the New York Heart Association functional class IV. The study observed a significant association between serum intact parathyroid hormone (PTH) levels and various clinical parameters in patients diagnosed with heart failure (HF). These parameters included B-type natriuretic peptide (BNP) levels, left ventricular ejection fraction (LVEF), heart rate, creatinine clearance, left atrial size, left ventricular diastolic diameter, diuretic usage, presence of atrial fibrillation, and hemoglobin levels. Based on the analysis of the receiver operator characteristic curve, it was determined that a PTH cut-off value of >95.85 pg/ml is optimal for predicting advanced HF. This cut-off value yielded a sensitivity of 94.15% and a specificity of 65.24%. Conclusion: we concluded that the serum parathyroid hormone (PTH) levels has the potential to offer additional valuable insights and serve as a straightforward biomarker approach for classifying individuals with advanced heart failure (HF) who exhibit elevated PTH levels.