How reliable are smartwatches for heart monitoring? Ambitious runners Florian and Leo want to find out for sure — and compare the ECG function of their fitness trackers with a professional electrocardiogram performed by a cardiologist.

Can the watches actually detect cardiac arrhythmias? And how useful are they for preventive health care? Cardiologist Dr. Jürgen Fritsch evaluates the results and explains why a medical examination remains indispensable for accurate health diagnoses despite modern technology.