I have aortic valve stenosis and am wondering if lifting 10lb dumbbells is bad?

VALVE AREA? Depends on the valve area, transvalvular gradient, contractility, ejection fraction, left ventricular end diastolic and systolic dimensions, and overall physical conditionig. Need echo findings, blood pressure and heart rate and transvalvular gradients.
Ask cardiologist. Your cardiologist knows the specifics to your case. Generally, if asymptomatic, and the valve area is more than 1.5 cm, it should be okay. Check to have your doctor review any exercise program to be safe.