9 July 2013 Last updated at 19:11 ET
By Michelle Roberts Health editor, BBC News online
Air pollution is harming people with weak hearts – even killing them, a big international study reveals.
Experts estimate the toll includes thousands of Britons each year.
The British Heart Foundation, which funded The Lancet work, says the UK must clean up its air – many of its cities often exceed safe levels set by the European Union.
The government has already admitted that in 15 regions, air quality will breach EU limits until 2020.
But Defra says it is committed to improving air quality and that most parts of the UK meet EU air quality limits for all pollutants.
Air pollution, largely from traffic fumes, has previously been linked to heart attacks but not heart failure.
This happens when the heart muscle becomes weak and less good at its job of pumping blood around the body. It is often the consequence of a heart attack and affects more than 750,000 people in the UK.