Yes, from what I read trans-dermal application is way more effective than supplements. While supplements will add magnesium to your body, from what I read only a fraction of the amount written on a bottle will be absorbed into your body.
It contains 33% magnesium chloride, which is the right type of magnesium, and according to the text it comes from the same ancient source, so I think this is the right stuff
Palpitations are feelings that your heart is skipping a beat, fluttering, or beating too hard or fast. You may have these feelings in your chest, throat, or neck. They can occur during activity or even when you're sitting still or lying down.