No. This is one of the most important and least understood facts about sudden cardiac arrest. In many cases, SCA is the first indication that anything is wrong with the heart at all. The person may have had no previous cardiac diagnosis, no symptoms, and no reason to believe they were at risk.
This matters because it changes how we think about prevention and response. Waiting for someone to show signs of heart disease before taking SCA seriously is not enough. Around 80 per cent of out-of-hospital cardiac arrests in the UK are witnessed by a bystander, most of whom have no medical training. The single most important thing any bystander can do is start CPR immediately and use a defibrillator as quickly as possible, regardless of whether the person has a known heart condition.
Some underlying conditions do significantly raise the risk of SCA, including inherited cardiac conditions such as HCM, Long QT Syndrome, and Brugada Syndrome, many of which go undiagnosed for years. This is one of the reasons family screening after a cardiac arrest is so important.