Hi There, I Have Been Taking Half Tablet Of Monomal

Hi there, I have been taking half tablet of monomal 60mg for several months, then on 28th December 2016, my doctor sent me to hospital by ambulance because I was having chest pain. (I have angina and AF). The hospital doctors changed my monomial to isosorbide-5-mononitrate 60xl tablets, one whole tablet a day. This evening I got a pain in my chest like I have had previously, is it alright to take my GTN spray.