This fluttering in all likelihood is due to muscle and is unrelated to the heart. A strong muscular contraction during the vomiting and some electrolyte imbalance are the most likely cause for the fluttering which is also called as muscle fasciculation or twitching. The one or two strong muscle contraction can cause residual muscle fasciculation persistently or episodic for next few days.
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I would be happy to assist you further, if you need any more information.