To identify heart failure (HF), natriuretic peptides were frequently measured. Their levels were also higher in people with atrial fibrillation (AF). For a study, researchers examined natriuretic peptides in unselected patients with cardiovascular diseases for a study. They connected their concentrations to AF and HF state and outcomes to better understand their value in predicting future cardiovascular events. Clinical examination, 7-day ECG monitoring, and echocardiogram were used to diagnose AF and HF in patients with cardiovascular problems who presented to a big teaching hospital. The N-terminal pro-B-type natriuretic peptide (NTproBNP) was measured centrally. About 4 NTproBNP groups were defined based on a literature review (<300, 300–999, 1000–1999, and ≥2000 pg/mL). NTproBNP concentrations and clinical features were linked to HF hospitalization and cardiovascular death. In 1,616 of 1,621 patients (99.7%), follow-up data were available, and analysis was completed after 2.5 years (median age, 70 [interquartile range, 60–78] years; 40% women). HF hospitalization or cardiovascular death increased from 36 of 488 (3.2/100 person-years) in patients without AF or HF to 55 of 354 (7.1/100 person-years) in patients with AF alone, 92 of 369 (12.1/100 person-years) in patients with HF alone, and 128 of 405 (17.7/100 person-years) in patients with AF plus HF (P<0.001). In patients with AF only (C-statistic, 0.82; 95% CI, 0.77–0.86; P<.001) and other phenotypic groups (Cstatistic in AF plus HF, 0.66; [95% CI, 0.61–0.70]; P<0.001), higher NTproBNP concentrations predicted the outcome. Elevated NTproBNP concentrations, regardless of the presence of HF, predict future HF episodes in patients with AF, promoting routine quantification of NTproBNP in the assessment of patients with AF.