How fast must a heart beat for it to be lethal?

A lethal heart rate depends on several factors, including the individual's age, overall health, and underlying heart conditions. However, generally, a heart rate that exceeds 220 beats per minute (bpm) for a prolonged duration can be considered potentially lethal. Such extreme heart rates can disrupt the heart's normal rhythm, leading to ventricular fibrillation (VF) or ventricular tachycardia (VT), both of which can cause sudden cardiac arrest and death.

It's important to note that lethal heart rates can vary among individuals, and underlying heart conditions can make a person more susceptible to the adverse effects of high heart rates. Therefore, it is crucial to consult with a healthcare professional if you experience excessively high or abnormal heart rates to assess and manage the underlying cause.