In any case, if your heart starts to feel uncomfortable and you feel like you're going to pass out, take a long, deep breath and cough vigorously without stopping. Continue to cough from the base of your chest, as if you are trying to cough up wet phlegm deep in your chest. Cough every 2 seconds, without holding your breath, until medical help arrives or your heart returns to normal.
Taking long, deep breaths increases oxygen to the lungs, while coughing "squeezes" the heart, spreads blood, and starts working the heart.
This approach gives people with heart failure valuable time to wait for an ambulance or go to the hospital, and knowing this will save many lives.