What Causes Dizziness And Severe Headache?

Hi
My mother is 92 and well. Recently after having light headedness and pounding headaches the Doctor found her pulse was 166 pm! He put her on medication which brought it down to 108. An appointment was made for her to see the Cardiologist. He put her on warfarin for approx 5 weeks and wants to take her in to restar her heart. She returned to her own home after that (She was staying with me for 3 months) and her own G P is looking after her (very well, might I add) She is having her blood checked every 3 days and today the Dr said to stop the warfarin for 3 days until it would be checked again as it was not good (The blood?? Or what?) She thinks he said it was 6.1

I am totally lost as to what is going on at this point. Can you explain to me please exactly what is going on and what the doc is doing?

Thank you very much

Regards

Dorothy

What does this all mean?