I Got Concor Cor 2x1.25 To Treat Tahicardia, But After

I got Concor cor 2x1.25 to treat Tahicardia, but after 7 day if use my puls was sometimes under 60. After that my dr told me to take 1,25 once per day.How can I stop use this medecine. I take it just two week.My puls goes sometimes under 60 even with 1 per day.I had very stresfull period that caused pulse 115 one day when I went to mefical office.
Thank you for help.
Ana Korac from Serbia