The heart is a biological wonder . It beats roughly 2.5 billion times in an average lifetime. Unlike skin cells, which regularly die off and regrow, a healthy adult heart hardly regenerates at all—even through all the wear and tear. The heart has another superpower: Resistance to tumors. Nearly every tissue in the body turns cancerous, but the heart almost never does. Cancers in heart tissue show up in less than 0.3 percent of autopsies, or about 1.5 cases per million people each year. How the heart keeps cancer at bay has baffled researchers. Pinning down its hidden defenses could inspire treatments for more vulnerable tissues, including top killers such as breast, lung, or colorectal. Persistent mechanical strain may be the key. A new study from the University of Trieste suggests that with every beat, the heart pushing against pressure dampens gene activity tied to tumor growth.…