@gloaming Thank you so much for replying so quickly. I was given the tartrate for instances when my HR exceeded 100 for over 10 minutes. This happened around 1:30 this morning--ramping up to 120 (I know that's not high for many people, but it felt like my heart was rocketing out of my chest, to me; the HR of 108 woke me up from a sound sleep). So the tartrate was Rx'd for only such incidents as that, of which there've been very, very few. (For some reason, nitroglycerin was Rx'd and then removed from my meds.)
I was Rx'd succinate to take daily.
I was writing to find out if it would be dangerous to overlap these meds' periods of effectiveness. Since then, I've had a call from my doctor's nurse at about 9:15. She assured me, after checking with my cardiologist, that it was OK, and that I could go ahead and take the succinate. She was going to check back with him to see if he had an alternative to tartrate in mind for instances of HR excursion above 100, sustained for 10 or more minutes.
I understand that succinate is the entire daily dose--it's in extended-release form--for 24 hours. However, there are rare occasions when my HR exceeds a threshold and time period *during a period of inactivity*; my doctor was worried about those periods.
(UPDATE: I'm waiting to see if he has something in mind to replace tartrate and hope to hear from the nurse this morning sometime.)
Thank you again for such a prompt reply!! 🙂