Does a bag of mag belong in rapid AF? Right drug, wrong expectation. We turn the belief dial through Davey & Teubner 2005, Ho 2007, LOMAGHI, Chu 2009 and MAGMAR. Take-home: rate, not rhythm; alongside, not instead; 20 mmol (about 5 g), not 36 mmol (about 9 g). Doses in Australian chart units. Re-recorded 10 Oct 2026. Teaching content only, not clinical advice.