As @jachrist explained perfectly, it's gradual. The speed at which this happens varies as each of us is different. I was sorry to read that he needed to take the long journey before getting the proper diagnosis. That underlines the point that a cardiologist well-versed in HCM needs to be found to oversee your care. The problem for many is getting that proper diagnosis in the first place! To further explain the echocardiogram, it clearly shows where the HCM/HOCM is occurring and mine showed the increase in thickness yearly over time.