Lee Charlie/Shutterstock.comAs a cardiologist, I frequently meet patients who have stopped taking medicines that could keep them alive. Often it’s because they’ve seen a dramatic headline or a worrying TV report about a drug they rely on. But sometimes, patients are right to pay attention: new studies really can overturn decades of medical practice.Few drugs illustrate this tension better than beta blockers. Long prescribed after heart attacks, these medicines can be life-saving for some people, helpful for others and useless – or even harmful – for the rest.Beta blockers have been used for more than 40 years in almost all patients with heart attacks. But this practice was based on studies done before modern treatments were available, and before we could detect very small heart attacks that do not affect the overall function of the heart.Recently, two studies on beta blockers in patients with heart attacks were reported in the news. The Spanish-Italian study received the most attention. Media reports suggested that most heart attack patients did not benefit from beta blockers, and that in women the drug might even increase the risk of hospitalisation and death. Reports like this can make people stop taking their medication. At the same symposium in Madrid, the second study – which got less attention – showed almost the opposite. Patients with heart attacks did benefit from beta blockers. And if there were differences between the sexes, women might actually have had more benefit than men.The heart of the matter: ejection fractionA key to understanding the different results is something called the left ventricular ejection fraction. This is the percentage of blood in the left chamber of the heart – its main pumping chamber – that is pushed out into the body with each heartbeat. Normally, ejection fraction should be at least 50%.If we look at all the studies together, including one I led and presented last year, the picture becomes clearer. Patients with an ejection fraction of 50% or higher after a heart attack do not benefit from beta blockers. But patients with an ejection fraction below 50% do benefit. And this is true for both men and women.The European guidelines from 2023, as well as the recently published American guidelines, still recommend beta blockers after most heart attacks. Many doctors are therefore reluctant to change a therapy tradition that has been in place for 40 years. Ejection fraction explained. My colleagues and I are now planning to pool data from the recent large studies on patients with heart attacks and an ejection fraction of 50% or more. The results, expected later this year, will probably give definite answers about beta blockers in this population and change future guidelines.But many patients clearly benefit from beta blockers, including those with heart failure and reduced ejection fraction (with or without a prior heart attack), angina pectoris (chest pain caused by reduced blood flow to the heart), or various heart rhythm disturbances. Beta blockers can also be prescribed for other reasons, such as high blood pressure, migraine prevention, tremors, as well as off-label use for stress and anxiety. For patients, it’s not easy to know all the reasons why beta blockers are prescribed, and in some cases, they may not be suitable at all. So I’ll end with a good, if not very novel, piece of advice: always consult your doctor before making any changes to your medication.Tomas Jernberg's employer (Karolinska Institutet) has received a grant from MSD for a research project performed by Dr. Jernberg but not related to this article.