Is OTHER wrong in the post ? POST : Relevant to this situation is that my (26M) girlfriend (21F) has a severe heart condition, underwent two heart surgeries, is on several medication for it and has to be very careful about not getting stressed and/or scared due to how frequent her afib attacks are.

My best friend (22M) is aware of this and has known her for the duration of our relationship (2 years) and known me for 4 years. 

Recently he has been in a good mood and I guess became energetic, and started jump scaring my girlfriend at random times during the discord calls by making loud sounds very close to the microphone or shouting down the microphone when entering the chat. Perhaps he found that funny.

In fact, a few days ago as he entered the chat he screamed down the microphone and it gave her chest pains. She didn't want to say anything because she didn't want to be rude and asked me what to do about it as it became more repetitive as the days went on until one time he did it when I was in the call.

I politely asked him to stop but he proceeded to do it again twice after that - each time I asked him to stop. I left the call after the last time and told him I won't be coming back until he stops this as it very disrespectful to her and dangerous.

She didn't want to start an argument and said that she can deal with it but I didn't think she should. 

He then sent me a half assed apology and once again I said that as long as he didn't do it again we were fine. He made a sarcastic remark to which I told him he cannot see that he is in the wrong and is making us both uncomfortable with his actions.

He constantly kept dismissing me and later resorted to personal insults and gas-lighting me saying that I'm causing issues on his birthday (which it is, but that doesn't give him the right to disrespect my girlfriend) until I snapped, blocked him and told him to fuck off.

My girlfriend got a message from him asking her why I was overreacting about this. AITA in this situation? Did I overreact?

TL;DR
My best friend kept jump scaring my girlfriend knowing she had a heart condition and then when confronted about it became confrontational, gas-lighted and insulted me until I snapped, told him to fuck off and blocked him.