If my father had hypertrophic cardiomyopathy, how likely will it be that my son has it too?

Don't know: Hypertrophic cardiomyopathy does have a genetic component and what i found says it is passed on from parents. "the condition is present from conception and excessive growth of the muscle may begin before birth when the foetal heart is developing". If you are concerned the best course of action is to see a cardiologist who can do an echocardiogram which is the gold standard for diagnosis.

Depends on you: If you inherited it from your father, your son could be at 50% risk. If you do not have it, his risk is low.

25%: Generally, hypertrophic cardiomyopathy is inherited in an autosomal dominant fashion. In other words, an affected individual has a 50% chance of passing the abnormal gene to each of their children. I assume you do not know your status regarding hcm. The math is that you had a 0.5 likelihood of inheriting an abnormal gene, and your son, if you are affected, has a 0.5 likelihood. .5x.5=.25=25%.