The aim of this study was to investigate changes in heart rate during submaximal exercise as an index of cardiovascular function in older adults participating in the Groningen Active Living Model recreational sports programme who were sedentary or underactive at baseline. A repeated measurement design was conducted; 151 participants were included, providing 398 heart rate files over a period of 18 months. Multi-level analyses were conducted; growth and final models were developed. Significant decreases in mean heart rate over time were observed for all walking speeds. The covariates of sex and body mass index (BMI) were significantly related to mean heart rate at each walking speed, except for BMI at 7km center dot h-1. No significant relationships were observed between energy expenditure for recreational sports activities and leisure-time physical activities and mean heart rate, except for energy expenditure for leisure-time physical activities at 7km center dot h-1. From baseline to December 2002, decreases in predicted mean heart rate were 5.5, 6.0, 10.0, and 9.0 beats center dot min-1 at walking speeds of 4, 5, 6, and 7km center dot h-1; relative decreases ranged from 5.1 to 7.4%. Significant decreases in heart rate observed during submaximal exercise reflected a potential increase in cardiovascular function after 18 months of participation in the Groningen Active Living Model recreational sports programme