The higher a student's heart beat increases during an examination, the more likely they are to achieve better result, according to new research.
The survey, undertaken by AQA exam board, found that on average the most successful pupils' heart beat reached a level that was 23.9 beats per minute (bpm) faster than normal.
And those who performed at the bottom end of the class were found to have a minimal increase in heart beat - only around 3.9bpm more than their normal rate.
One of the leaders of the research, Suzanne Chamberlain, said: "This increase in heart rate is a sign that arousal encourages them (the students) to be more alert. It encourages them to work to the best of their ability, it sets the scene for better performance."
The students were fitted with heart monitors in the hours before the exam. For the highest performers, their heart rate increased from 79.8 beats a minute to 103.7 while sitting the exam. And the pulses of those who did not fare as well - their rate only went up slightly, from 78.5 to 82.4.
But the study does not recommend that those taking exams use stimulants to boost their heart rate.