Is it safe to have sex if you have tachycardia?

It depends.: Although there are some people with a mild tachycardia due to a benign condition termed autonomic nervous system dysfunction (dysautonomia), most tachycardias have an underlying specific cause. Therefore, before answering your question, it would be best to undergo a medical exam to search for that cause. It could be an overactive thyroid gland, infection, fever, a rare tumor or some other problem.