I have tachycardia and take metoprolol 25mg once a day. i was wondering if ill be safe to take cbc oil. ?

CBD oil: Do you mean CBD(cannabinoid oil)? I don't believe that CBD would interact with metoprolol or provoke tachycardia.Your pharmacist can inspect your product and possibly provide more information about your CBD oil, interactions and adverse effects,if any.

No simple answer : Cannabidiol (CBD) is one of over 60 natural compounds from the Cannabis sativa plant for which humans have cellular receptors. That CBD has significant effects on various body systems is undeniable. Unfortunately, few are well studied. If your tachycardia is mild and from being a "nervous person" is very different than if you have a problem in your heart's electrical system. Need MD evaluation.

CBD should be safe: I presume you mean CBD oil. There are no known significant interactions between CBD and metoprolol. CBD is not likely to particularly help or hinder your tachycardia but has numerous other proven health benefits. Seek a full-spectrum CBD oil and start with low doses; most people do well on 20-30 mg 2x/day. See https://www.projectcbd.org/guidance/conditions for links to medical research on CBD.