If the palpitations are persistent, there is a method you can try called the Valsalva maneuver. To perform it, you need to hold your breath, block your nose, and attempt to breathe out as if you are blowing up a balloon or strain as though you are having a bowel movement. Hold this pressure for a few seconds and see if the palpitations have stopped. Repeat again if necessary. The build-up of pressure from the Valsalva maneuver puts pressure on the vagus nerve, which can slow your heart rate down.