Pathophysiology

Video
http://coursewareobjects.elsevier.com/objects/hao/anim/13-010ap.htm
http://www.med.yale.edu/intmed/cardio/echo_atlas/entities/aortic_stenosis_senile.html
3rd heart sound due to possible explanations include impact of the ventricle against the inner chest wall or a sound originating within the ventricular apex due to sudden limitation of longitudinal expansion.
4th heart sound due to forceful atrial ejection.
Pathophysiology of causes:
Calcium buildup on the valve. Calcium deposits result in stiffening of the leaflets of the valve.
Rheumatic fever. Rheumatic fever may result in scar tissue forming on the aortic valve. Scar tissue alone can narrow the aortic valve and lead to aortic valve stenosis.
Congenital heart defect.
Aortic valve narrows due to the causes above.
The blood flow of ejection is disturbed, causing a loud ejection systolic murmur.
The ventricles then have to hyperthrophy to compensate for the decrease in output. However, in the long run, the ventricles dilate and this decreases the compliance of the ventricles. The atria has to pump harder to fill the ventricles, thus the 4th heart sound.
Edema in lungs is due to backflow of blood.
Explanation in detail in PCL 