I happened to awaken kundalini in January and noticed my heart "flutter" over the past few days. This surely isn't a medical issue but feels like the heart "unclenching" with pleasurable "spurts" and "sprinkles" of prana being released repeatedly - it almost feels ticklish and borderline blissful.
I have a strong pumping heart, inherited. I suggest you also have one. I can always see it bump even if I wear a thicker shirt. I have experienced similarities, it could be quite intense, like an inner animal but a comfortable one.