Does taking magnesium help with heart palpitations and atrial fibrillation? how does it take work after taking it?"

It can help.: It helps, if ones magnesium level is low. In fact, in some people with life-threatening ventricular arrhythmias, intravenous magnesium can be life-saving. Raising the magnesium level can also prevent or treat supraventricular arrhythmias such as atrial fibrillation.

Complex, Mixed Data: All muscle cells water inside & outside separated by fat (~30% cholesterol: stabilizes & allows movement without tearing) membrane. Proteins in membrane pump na+ ions out, k+ ions in, along with other ion movements. Other proteins suddenly change this: allow na+ to go in & k+ out ~0.001 sec later. Inner membranes keep ca+2 away from contractile proteins to stop contraction. ↑mg+ may ↓irritability.