Leisure time physical activity, or exercise, has been described as today’s best buy in public health. Physical inactivity is responsible for around 10% of all deaths and physical inactivity costs global healthcare systems billions of dollars each year. Here, we describe the human and economic costs of cardiovascular disease. Then, we explain that physical inactivity is a major modifiable risk factor for cardiovascular disease. The evidence of the role of physical activity in the primary prevention of cardiovascular disease is reviewed and we make the case that exercise is medicine.