Hi XXXXXXX

Thank you for posting your question here.

Your granddad has what is called a tachycardia. It can be caused my many things including acute anxiety states and thyroid disease. In his case though I suspect the cause might be a small myocardial infarction or heart attack given his history.

Tachycardia of itself is not serious. It depends on the underlying cause. Your grandad is in the best place possible.

I wish him well and hope he makes a full recovery quickly.

If you have any further questions please ask me. Otherwise I hope you can accept this answer.

Thanks.

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