Credit: zsv3207/Getty The beating of the heart stops cancers from growing in this organ in mice, reports a study published today in Science 1 . This could explain why tumours affecting the heart are so rare in mammals, including in people. Almost all organs and tissues in the body can develop tumours, but cancers that affect the heart are seldom observed. In people, primary cardiac tumours have been identified in fewer than 1% of autopsies, while secondary cancers, in which the primary tumour occurs in a different part of the body, have been found in up to 18% of autopsies. Until now, there has not been a satisfactory explanation for why cardiac tumours are so uncommon, says James Chong, a cardiologist and researcher at the University of Sydney, Australia. This latest study puts forward a compelling case that mechanical strain on the heart could be an explanation, he says.…