I took Tamoxifen for 20 months and have just switched to Femara for 2 months. When I took Tamoxifen, at the beginning, I had some heartbeat issue but not serious. I exercised a lot to "train up" my heart and the issue has gradually subsided to nearly nothing. I also have some mild hot flash which have subsided too. At the end, it's like taking a vitamin pill a day and I basically feel nothing. With Femara, save for some mild hot flash, I don't feel any side effect either.
Good luck with your hormonal treatment.