We do want to get into the mountains to see the incredible views, but my husband's cardiologist recommends we not ascend higher than 9,000 ft.
Looks like you live at or near sea level (NJ?). What experience has your husband had at higher elevations in the recent past? I ask because different people have wildly different reactions to higher altitude, even people without any known heart disease complications, and from my own personal experience, a doctor's recommended cutoff of 9,000 feet seems quite high - I would suspect your husband will have breathing difficulties at a much lower elevation than that, even below 5,000 feet.
I am in my late 60s, I am a heart patient, and for most of my life I lived at sea level or barely above it, and in the last decade when I retired I lived at 6,300 feet elevation in Colorado until for 7 years, and I currently live at near sea level now, and I had no issues whatsoever in Colorado, even when exerting myself, and felt no ill effects when we went much higher, up to around 10,000 feet elevation (Breckenridge, CO). Yet I have several very fit senior friends, much fitter than I with no heart disease, who when they made a similar move from sea level to Colorado and actually lived at a lower elevation than I, they suffered significant breathing difficulties, altitude sickness, etc. I have friends who did not fully adjust to living at elevation for a year or more.
The point being, you never know how any individual person will react to being at high elevation. Throw in any kind of exertion, including just walking around, and you may discover he should not attempt to go from sea level to 9,000 feet.
My only suggestion would be for him to try out spending a few days at a much lower elevation - say no higher than 4,000 feet or so - and engage in walking or whatever kind of exertion he does now, and see how that goes? Wengen is at around 4,000 feet; see how it goes there before venturing any higher - that would be my approach given his condition and the doctor's warning. I would even suggest spending a few days in say Interlaken, first, a little below 2,000 ft, and it is relatively flat there, easy to get around - he should do some brisk walking - see how that goes first? Because in Wengen, the town is not flat, even getting from the train station to your hotel can involve fairly steep inclines and challenging terrain.
Good luck.
