If the semilunar cusps of the pulmonary valves collapsed and were completely non-functional, what effect would this have on the right coronary artery?
Well, you'd probably die. But more specifically, if the semilunar cusps of the pulmonary valves were non-functional then a potentially large portion of deoxygenated blood would retreat back into the right ventricle during ventricular contraction. This would result in improper cardiac output to the lungs and eventually reduced blood flow back into the left atrium. Reduced blood flow into the left atrium would mean reduced flow into the left ventricle and consequently, into the cusps of the aortic semilunar valve. Since the right coronary artery originates from the cusps of the aortic semilunar valve, over all inflow into the right coronary artery would be reduced, a potentially fatal disease. Similarly, blood flow to the left would also be affected.