What is the no-flow time and why does it kill people? No-flow means: there is no longer any blood flowing in the body—most often because the heart is no longer pumping effectively due to an acute illness. This is especially harmful to the brain. The brain requires 20–25% of our blood flow and thus our oxygen; relative to its own weight of only about 1.3 kg, this is a great deal. After 5–10 seconds without blood flow, the brain ceases to function, meaning the affected person loses consciousness. Many witnessed this live with the Danish footballer Christian Eriksen, who suffered a cardiac arrest on the football field. After 3–5 min without oxygen, the brain begins to die if no external measures are taken. In Germany, emergency services typically arrive after about 9 min, and in rural areas often much later. This is far too late for this emergency situation, which is why only about 10% of people who suffer such a cardiac arrest survive at all. Yet it is very simple for any bystander to take life-saving action in this situation and improve survival. These individuals must recognize the life-threatening situation and immediately begin chest compressions. This restores blood flow to the brain and keeps the brain alive.