There have been cases reported of healthy young athletes suffering cardiac arrest in the middle of a game or practice. This is likely to have been caused by unrecognised congenital heart disease or genetically inherited heart rhythm disorders, which can be hard to diagnose. Warning signs are often present. One is having dizzy spells or passing out during exercise. Next is a family history of sudden death. If you have a family history of heart disease, fainting or cardiac irregularities, get an ECG done. These tests are not foolproof, however. So if you experience shortness of breath, feel faint or have chest pain, stop exercising rather than push yourself to exhaustion. If you are over 40 and planning to run your first marathon, you should undergo a stress test. You’ll run on a treadmill or go on a stationary bike to measure your heart rate and blood pressure while you perform increasingly difficult levels of exercise. A healthcare professional will be there to observe your ECG for changes while you exercise. Alternatively, you may have a nuclear or echo stress test that examines the blood flow to your heart.