I usually experience palpitations around 7 days into a water fast, and find they tend to taper off by around days 12-13. So yes, I would say perfectly normal, if slightly disconcerting at first when you're not quite sure what's going on.
Unless you have some other underlying health issue, I would suggest it's not something to get too worried about. I agree with the suggestion that the likeliest explanation is the cardiac muscles adjusting to burning ketones rather than glucose.
I also found my BP doing strange things during fasting - mainly raised diastolic (ie BP 'at rest'), but lowered distolic pressure. Completely anti-intuitive, but according to Dr Andre Kruger (the 'fast doctor'), all perfectly normal & nothing to worry about.
Worrying is never good for BP anyway, is it? So relax, and enjoy.