I've Been Diagnosed With 100% Blockage Of My LAD, 3mm

I've been diagnosed with 100% blockage of my LAD, 3mm occlusion lower down the artery. But my collateral blood supply is strong to the extent that my 2D echo test show a very healthy heart . I did my Thalium stress test which confirmed the blockage but my blood supply would reduce to the blocked area only on high stress. I walked for 7 minutes on the machine but flat no incline, and the ECG showed some changes. My cardiologist explained that your Heart is challenged only under stress and you can live normally without exercise etc.
My question is do i need to put a stent to open the blockage? Can i travel without putting a stent to high altitudes.