with regards to the other user's comment, they are not wrong in that there are medications that can cause tissue necrosis, and this being the circulatory system that can include the heart.

but in re estradiol specifically (and steroids in general), we tried looking but weren't able to reach any meaningful conclusion about any tissue necrosis.

there doesn't look to be much literature surrounding this topic, at least that we could find anyways. there is this review, which provides examples of medications that while causing pain and discomfort when accidentally injected into a vessel otherwise did not result in considerable complications. there are of course other cases with other medications that went far worse, but notably there didn't look to be any steroidal medications among them. the only thing we can really conclude is that tissue necrosis in the heart is not a given. but this doesn't mean it's out of the question entirely either.

this tutorial about accidental intra-arterial injections states:

Whilst the exact pathophysiology is unclear (and likely varies by drug) thrombosis is believed to represent a final common pathway. This may then lead to tissue ischaemia and necrosis.

the whole thing appears to be a very broad generalization, one that surrounds a) some medications often used in hospitals and what to do if a medic mistakenly injects something into a vessel, and b) illicit drug use. but again, there is nothing in specific about estradiol or any steroids.

otherwise the most specific stuff we could find were anecdotes from online forums, which frequently mentioned elevated heartrate, it feeling awful in general, but often not being problematic beyond that. most of these accounts were about testosterone, which is a different drug, but it is also a steroid; the number of molecules injected was also more numerous than you would ever do in pretty much all of those internet posts we read.

there isn't a satisfying answer—there is only a considerable lack of information. with what little is out there though, we'd guess that you won't die and that you might be just fine given some time and caution, albeit getting checked out by a medical professional is still a good idea. well either that or more likely from your description you just punctured a vessel of some kind.

stay safe, stay comfy, and keep calm!

I agree with the top comment of this thread. I had an injection the other night that hurt more than usual and some of the actual liquid pushed back out the injection site. Still a bit sore a day later. I just didn’t fully relax my leg I think. Something like that. Some combo of not getting the needle far enough and my leg being a bit tense. I was kind of rushing so maybe that’s part of it. Wasn’t really able to do the regular ritual.

Definitely monitor and such. Doesn’t seem so out of the ordinary that you need to out yourself to you doctor right away, but seek medical attention if it doesn’t improve from how you described it. Like bruising hopefully starts to fade from here on out.

Could go to an urgent care or something that isn’t your doc?? Just say it happened with your prescribed meds or something. Should be able to keep those records separate if you play your cards right. Some folks might have thoughts on that for other reasons, but it’s always something I keep in the back of my head if I am ever doing DIY.