Everything @houston13 says. An ascending aortic aneurysm at 4.6 cm is not small, and the fact that it’s in the ascending aorta matters. That segment of the aorta is exposed to the highest pulsatile pressures in the body. Unlike the abdominal aorta, the ascending aorta sits inches from the heart and takes the full force of every systolic beat. Growth rate matters, but so do transient pressure spikes.

Scuba diving raises a few specific concerns for people with ascending aortic disease. The biggest is not ambient pressure itself, which increases gradually with depth, but what divers often do unconsciously: breath-holding, straining, heavy finning against resistance, awkward gear handling, and sudden exertion on the surface or during ascent. All of those can trigger a Valsalva-type maneuver that acutely spikes blood pressure. That kind of spike is exactly what stresses the ascending aorta and the aortic wall. Depths around 100 feet also increase gas density and breathing resistance, which can subtly encourage breath-holding or forceful exhalation. Add cold water, task loading, current, or stress, and the physiologic load goes up further. None of that shows up on a stress test in a lab.

I was physically fit when my dissection happened. No warning. No prodrome really. That’s why people like me tend to be conservative once the aorta declares itself. The fact that your team wants six-month surveillance is appropriate, but imaging stability does not mean zero risk in the interim. Dissections and ruptures are often triggered by momentary pressure events, not gradual enlargement alone. Calcium score and coronary plaque add another layer of cardiovascular risk during exertion.

Some people with stable, smaller aneurysms do continue diving under very controlled conditions, but that decision is highly individualized and usually involves explicit clearance from an aortic specialist who understands both diving physiology and ascending aortic pathology. Many general cardiologists simply don’t see enough dissections to fully appreciate how unforgiving the ascending aorta can be.

If I were in your position, I would be asking very direct questions: what blood pressure limits are safe, whether beta-blockade is optimized, whether any activity involving breath control or straining is advisable, and whether shallow, no-stress, no-current dives are materially different from deeper recreational profiles. I would also be brutally honest with myself about how disciplined I can truly be underwater.

I’m not a physician, but I am someone who survived a Type A aortic dissection in 2015 that came out of nowhere and required emergency open-heart surgery with a Dacron graft of my ascending aorta and arch. So I look at questions like this through the lens of lived experience, anatomy, and risk management.
I don’t say any of this to be alarmist. I say it because I survived, and I know how fast things can change when the ascending aorta fails. Knowing about the aneurysm gives you power, but it also calls for respect. Whatever you decide, I hope you make it with full information and a margin of safety that lets you keep enjoying life for many years to come. Peace.