Hi Chantel,
I too have this and I would echo what others are saying about hormones! i'm 48 and started worrying about this as I noticed periodically that I'd feel a spike in pulse and a warm sensation. The weird thing was it usually occurred when I was sitting and not doing anything strenuous. I also have noticed it happening when I wake in the morning.
I know I am well into perimenopuase as I've just got 10 months without a period, (apart from a very light one) and last year went nearly 11 months again with only a light one in between. So I'm thinking it's hormone related as it settles and then I can go a while without it happening again.
Unfortunately, anxiety can also trigger these things which isn't helpful for us worriers as the more we focus on it the worse and more obvious it becomes.
If it's any consolation my peri menopuase journey started around 37 about your age. I had the flooding periods, then skipping for a month, then every two weeks along with random spotting but several scans confirmed it was just wonky hormones!
Honestly, the joys of womanhood! One thing that I would recommend is when you feel it happening, a nice big glass of cold water. I read that it helps to calm and cool you down and it works for me, also dehydration can add to an increase in heart rate , so lots of H20.
Take care