Heart rate monitors are central to new special fitness classes that are designed to improve the fitness of those with a history of heart problems.

Cardiac instructors run classes from health clubs in Dartford and Swanley that take into account each person"s health issues, reports Kent Online.

In particular, heart rate monitors are used to ensure that instructors know if participants are over-exerting themselves.

The sessions place a greater focus on exercises like running and cycling, with participants monitored while using treadmills and exercise bikes and also instructed to do longer warm-ups and cool downs to ensure that they are not overworked.

Fitness instructor Elaine Roles, who runs one the specialised cardiac rehabilitation sessions, said that having a heart attack is a "devastating experience".

However, she added: "Regular exercise for those with a history of heart problems not only adds years to their life expectancy but adds life to those years."

One of leading cardiovascular charities in the UK is the British Heart Foundation.

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