The British Heart Foundation is encouraging people to take part in its ninth annual Walkabout UK, which is supported this year by Ian Botham and sponsored by Shredded Wheat.
The foundation has organised 170 sponsored walks throughout the UK, which are scheduled to run until October.
The charity wants people to "get moving
and discover how much fun they can have while taking part in physical activity.
A TV campaign featuring legendary cricketer Botham is running to help promote the national event.
The 20-second ad, which was funded by Shredded Wheat, shows Botham with his hand on his heart and the strapline "Help a heart - take part".
Slots have been booked on ITV, Channel 4, Channel 5 and satellite TV.
The ads will be screened during programmes including ITV's Coronation Street and breakfast show GMTV.
Special packs of Shredded Wheat, which bear the British Heart Foundation branding and details of the event, carry a £5 token. The foundation will receive an additional £5 from the cereal manufacturer upon successful completion of a walk by a participant.
Merchandising units carrying the special Shredded Wheat packs are appearing in Sainsbury's stores across the UK.
Roland Bush-Cavell, corporate marketing manager at the British Heart Foundation, said: "Millions of Shredded Wheat consumers and the general public are invited to take part and raise funds for the British Heart Foundation. We hope to raise more than £300,000."
All monies raised from Walkabout UK will help the foundation continue to fund pioneering heart research, as well as raise awareness of the importance of heart health.