Ive been on Tenormin for 6 years for an irregular heart beat. Recently it stopped being effective and I would have periods of 140 beat/per minutes rates. Yesterday I went to my PCP and she prescribed Diltiazem. Told me to start taking it immediately and stop the Tenormin. I took a dose last night, one this morning and one just about an hour ago. I feel like crud! Heart rate goes from 70 and regular to 80 and irregular, 120 for a while. I feel wiped out. Anyone with experience with Diltiazem/Cardizem?