Making sure you get enough exercise in midlife will help protect your heart, according to research.
Even those who make the switch in their late 40s and 50s can still benefit, the study of over 4,000 people suggests.
And it need not be hard toil in a gym - gardening and brisk walks count towards the required 2.5 hours of moderate activity per week, say experts.
But more work is needed since the study looked at markers linked to heart problems and not heart disease itself.
And it relied on people accurately reporting how much exercise they did - something people tend to overestimate rather than underestimate.
In the study, which is published in the journal Circulation, people who did the recommended 2.5 hours of exercise a week had the lower levels of inflammatory markers in their blood.
Inflammatory markers are important, say experts, because high levels have been linked to increased heart risk.
People who said they consistently stuck to the recommended amount of exercise for the entire 10-year study had the lowest inflammatory levels overall.
But even those who said they only started doing the recommended amount of exercise when they were well into their 40s saw an improvement and had lower levels of inflammation than people who said they never did enough exercise.
The findings were unchanged when the researchers took into consideration other factors, such as obesity and smoking, that could have influenced the results in the group of UK civil servants who were included in the study.
Dr Mark Hamer, of University College London, who led the research, said: "We should be encouraging more people to get active - for example, walking instead of taking the bus. You can gain health benefits from moderate activity at any time in your life."
Maureen Talbot of the British Heart Foundation, which funded the work, said: "Donning your gardening gloves or picking up a paint brush can still go a long way to help look after your heart health, as exercise can have a big impact on how well your heart ages.
"This research highlights the positive impact changing your exercise habits can have on the future of your heart health - and that it's never too late to re-energise your life.
"However it's important not to wait until you retire to get off the couch, as being active for life is a great way to keep your heart healthy."