Can you join the military with aortic stenosis murmur?

Unlikely: If you have aortic stenosis, your exercise capacity will be somewhat limited (depending on the degree of stenosis), so it's unlikely you will be able to join the military.

Regulations: " current or history of all valvular heart diseases, congenital or acquired, including those improved by surgery, are disqualifying. Mitral valve prolapse or bicuspid aortic valve is not disqualifying unless there is associated tachyarrhythmia, mitral regurgitation, aortic stenosis, insufficiency, or cardiomegaly.".