Common drugs such as Prozac, the COX-2 painkillers and beta blockers come with a major side effect that nobody has ever reported before - they stop the body's ability to protect you from a fatal heart attack. Scientists made the surprise discovery when they tried to understand why it is that someone who has had a heart attack is more likely to survive a second attack than someone who has never had an attack before. Apparently, after a first attack - assuming it's not fatal - the body begins a process known as 'ischemic preconditioning', where blood flow is restricted temporarily while cardiac tissues begin to strengthen. It's all triggered by a molecule known as the mitochondrial ATP-sensitive potassium channel. But the research team, from the University of Rochester Medical Center, discovered that some drugs - and especially the antidepressant Prozac, the COX-2 painkillers and the beta blockers - stop the molecule from doing its job. Therefore, people taking any of these drugs are more likely to suffer a second, fatal attack. The drugs have never before been linked to heart problems, but then again, nobody has been looking, say the researchers. (Source: Circulation Research, published online, February 25, 2010; doi: 10.1161/CIRCRESAHA.109.215400).