The decline in glomerular filtration rate (GFR) associated with aging is one of the most important predisposing causes of kidney failure in old age. Identifying persons at risk for accelerated GFR decline is an essential first step in the development of preventive measures to preserve kidney function in the elderly. Heart rate (HR) has not yet been studied as a risk factor for GFR decline in the general population. In the RENIS-T6 (Renal Iohexol-Clearance Survey in Tromsø 6), we measured baseline ambulatory HR and GFR as iohexol clearance in a representative, middle-aged cohort of 1627 persons without self-reported diabetes mellitus, cardiovascular disease, or kidney disease. In the RENIS-FU (RENIS Follow-Up Study), we repeated the GFR measurements and calculated the rate of GFR decline in 81% of the participants after a median follow-up of 5.6 years. The unadjusted mean rate of GFR decline was 0.96 mL/min per year. In multivariable-adjusted linear mixed models, 10 bpm higher ambulatory 24-hour and daytime HRs and office HR were associated with steeper GFR decline rates of 0.20 to 0.21 mL/min per year ( P=0.01). The odds ratio for predicting a rate of GFR decline twice that of the population mean in a fully adjusted model was 1.24 ( P=0.01) for ambulatory 24-hour HR. Office HR was also an independent predictor of a steeper rate of GFR decline. HR may be a useful biomarker to identify persons at risk of accelerated GFR decline.