In many cases, muscle thickening begins early in adolescence or adulthood. Nearly half of all people with HCM have evidence of heart muscle enlargement by age 30. However, muscle thickening can start at any age, and roughly 1 in 4 people do not develop structural evidence of HCM until age 60.
Symptoms of HCM may not be present when HCM develops or may be mild. Even after heart thickening begins, people may not notice symptoms for several years or decades.