Watch this video about heart attacks on HowStuffWorks. Heart attacks are the leading cause of death in our country, and the statistics are frightening, 95% of all cardiac arrest victims die before they can get to a hospital. American Heart Association (AHA) studies show that an impedance threshold device, which is about the size of a human fist, doubles the amount of blood flow delivering oxygen to vital organs, increasing a cardiac arrest victim's chances of survival. See how EMTs and doctor can save people from heart attacks.