Thanks for your question on HCM. By your description I think your husband is having large , chronic pulmonary embolism in major pulmonary arteries. And if it is large enough to occlude blood flow than surgery is the only option. And yes, surgery is very risky. Because already lungs and heart are weakened due to clots. So it is considered as major surgery with very very high risk intra operatively as well as post operatively. So need to discuss outcomes in depth with your treating surgeon.