If your tachycardia is due to an insufficient due to not eating properly its probably because your iron intake is low. good sources for iron intake are red meat or dark leafy vegetables high in Iron. Multivitamins or even iron supplements (Slow release iron) is helpful. Iron is responsible for carrying and binding oxygen to red blood cells. Low Iron = low absorption of oxygen = your heart needs to beat faster to supply your body with oxygen.
Replied by Chris
Raumati South, Wellington, New Zealand