As a fellow 6'4" + size person who loves sports/exercise, I was in your shoes a while back when I joined here. It shook my identity of who I am if I can't play basketball or lift a piano or squat etc....So I feel you for sure.

Good news is 6'4" puts you in an low risk category with a 4.3 size (https://www.jtcvs.org/article/S0022-5223(17)32769-1/fulltext) and this chart attached is helpful I found helpful from https://www.sciencedirect.com/science/article/pii/S0022522317327691#undfig1.

If it is quick growing and/or between 5 and 5.5 seem to be where the risk grows. We are both 6'4" and that is actually a benefit here for dissection risk and size.

I will state if they did not do a contrast CT, would advise it. Mine had the wrong size measured (smaller) with the non-contrast CT and echo (echo was closer though). It was actually in 5 cm range once measured with a contrast CT. Echos not considered a gold standard for measurement of this type of issue but is for Valve stuff. Also do genetic testing if you haven't got that scheduled already.

When it was believed to be smaller, it was recommend constant exercise without extremes. So biking was a check, sprints, mountain biking or hill runs through high grades was avoid if heart rate spikes or if I can't sing or talk. If I wante to do mountain or hills, use an ebike to keep the heart rate in a safe range. Lifting reasonable weight (lower amounts, more reps, don't hold your breath) check but not heavy lifting to increase blood pressure. Swimming constantly okay just no sprints. Yoga and Taichi and other slow flow stuff good but HIIT/Crossfit types of exercises are off the table. No combat sports or anything where someone could hit me in the chest like basketball. Etc, etc...You get the theme.

Consistent, measured exercise = safer/lower risk of a dissection
Fast heart rate or blood pressure spiking exercise or impact = higher risk dissection

For you, got to decide risk vs reward. Its a balance. Like you, I find a lot of community in sports and in intense exercise. Also I have read/heard athletes (https://www.acc.org/Latest-in-Cardiology/Articles/2024/09/09/10/21/CV-Sports-Chat-Dilated-Aortas-in-Athletes) and tall people just have a higher risk for these things for it appears no known reason if no family or genetic history has this. That sucks and I fall into this but it is a thing.

When I thought it was smaller and had to live with this for a long time before surgery, started a journey. First I had just slowed it down for a bit and shift my mentality while learning. Morned my loss of intense exercise and how it felt. Started to view it as a challenge a new way. Replace intensity with distance for example biking and swimming. Tried to keep my heart range steady in other exercises. I reached out to a science base trainer who actually had an anatomy background to discuss good ways to shift my lifting, training, and activity. One of the lifting changes discussed was lower weights, more reps and work on flexibility and moving up in weight slowly if at all. Also simply singing or talking during exercise to gauge exertion since I usually focus on the push. I did have to back off that one and stop lifting weights since my non-contrast CT and echo disagreed a lot in the size with each other during diagnose period and then due to my contrast CT basically moving me to a higher risk category. Before that though, found that it was possible to live a active, exercise focused life just with modifications and a different mentality.

You got this. You overcome challenges like you do in sport constantly. Hopefully my journey helps you feel a little better as you begin yours. Its a start of something new!