I take a daily multi vitamin tablet which contains 100mg of magnesium and eat a couple of bananas a day, while I also eat a lot of oily fish and tend to have a small portion of rocket with many of my meals.
About six weeks ago I read a thread on here about the beneficial effects of magnesium and decided to up my intake by taking a 500mg Magnesium Citrate tablet every day (they contained 80 mg of elemental magnesium).
After around a fortnight I entered a three week period where I became far more prone to ectopic and double and triple beats than I am normally. I've gone into full details of what happened in another thread, so all I'll say here is that the unusual heartbeats followed a regular pattern whereby they'd be absent during the nights and then last for much of the day after starting shortly after I'd had the magnesium tablet with my breakfast, before fading in the four or five hours before I went to bed.
About halfway through this three week period, I decided to stop taking the magnesium tablet and, around ten days ago, the unusual heartbeats stopped and have not returned.
I realise I should have run it by someone at my health centre before starting to take the magnesium tablets and will do so when I have my INR on Monday.
I've done some research and found that too much magnesium can cause heart palpitations, but the impression I got was that the quantities involved would have to be greater than I was taking, yet, to this non expert at least, the evidence points to the magnesium being the cause of them.