I recommend trying some coleus forskohlii. Forskohlii works very similar to cardiac glycosides slowing the heart rate, strengthening heart contractions and lowering blood pressure. It also stimulates the production of cyclic adenosine monophosphate (cAMP), which among other actions counters histamine responses. So it will address the palpitations and allergic reactions as well if present. Taking with a little nettle leaf or watercress will prolong the effects.