Coldness in chest in person of your age and background of aortic valve
and root repair may signify something serious. I assume your echo and Doppler examination did not reveal any significant gradient and there was no para valvular leak with the replaced valvular graft observed. Next step will be to decide whether your symptoms are due to coronary artery
disease or originating from from your food pipe (where your stomach contents+acid regurgitate and irritate). You need to consult a cardiologist
who will do an EKG and may recommend coronary angiography
alternatively you have to consult a GI specialist who will either diagnose the problem or refer you back to cardiologist.