Carbon monoxide is produced by faulty boilers, cigarettes and car exhausts and it is deadly at high levels as it "shoulder-barges" oxygen out of the blood, meaning less is transported around the body.
However, studies have indicated that even low levels, such as that found in built-up cities with lots of traffic, may also damage the heart. In the latest study, researchers at the University of Leeds found that levels common in heavy traffic could affect the way the heart resets itself after every beat because the gas kept sodium channels, which are important for controlling the heartbeat, open for longer.
Disrupting the sodium channels can disrupt the heart's rhythm, leading to cardiac arrhythmia, which can be fatal. Together with researchers in France they tested an angina drug – which also affects the sodium channels – on rats exposed to levels of carbon monoxide similar to heavy pollution, which had the same heart problems and found they could reverse them.
A spokesman for the British Heart Foundation said: "This study is a good example of research being used to better understand the underlying causes of an abnormal heart rhythm and in this case it has uncovered the ability of an old drug to perform a new trick. Carbon monoxide poisoning is tragically common but hopefully these promising results can be replicated in people so that it saves lives in the future."