Heart failure (HF) and atrial fibrillation (AF) are growing in prevalence worldwide. Few studies have assessed to what extent stage 1 hypertension in the 2017 American College of Cardiology (ACC)/American Heart Association (AHA) blood pressure (BP) guidelines is associated with incident HF and AF. Analyses were conducted using a nationwide health claims database collected in the JMDC Claims Database between 2005 and 2018 (n=2,196,437; mean age, 44.0±10.9 years; 584% men). No participants were taking antihypertensive medication or had a known history of cardiovascular disease. Each participant was categorized as having normal BP (systolic BP [SBP]<120 mm Hg and diastolic BP [DBP]<80 mm Hg; n=1,155,885); elevated BP (SBP 120-129 mm Hg and DBP<80 mm Hg; n=337,390); stage 1 hypertension (SBP 130-139 mm Hg or DBP 80-89 mm Hg; n=459,820); or stage 2 hypertension (SBP≥140 mm Hg or DBP≥90 mm Hg; n=243,342). Using Cox proportional hazards models, we identified associations between BP groups and HF/AF events. We also calculated the population attributable fractions (PAFs) to estimate the proportion of HF and AF events that would be preventable if participants with stage 1 and stage 2 hypertension were to have normal BP. Over a mean follow-up of 1,112±854 days, 28,056 incident HF and 7,774 incident AF events occurred. After multivariable adjustment, hazard ratios for HF and AF events were 1.10 (95% Confidence interval [CI], 1.05-1.15) and 1.07 (95% CI, 0.99-1.17), respectively, for elevated BP; 1.30 (95% CI, 1.26-1.35) and 1.21 (95% CI, 1.13-1.29), respectively, for stage 1 hypertension; and 2.05 (95% CI, 1.97-2.13) and 1.52 (95% CI, 1.41-1.64), respectively, for stage 2 hypertension vs normal BP. PAFs for HF associated with stage 1 and stage 2 hypertension were 23.2% (95% CI, 20.3%-26.0%) and 51.2% (95% CI, 49.2%-53.1%), respectively. The PAFs for AF associated with stage 1 and stage 2 hypertension were 17.4% (95% CI, 11.5%-22.9%) and 34.3% (95% CI, 29.1%-39.2%), respectively. Both stage 1 and stage 2 hypertension were associated with a greater incidence of HF and AF in the general population. The ACC/AHA BP classification system may help identify adults at higher risk for HF and AF events.