An anonymous online survey invited adult HCM patients to report participation in 11 activities (rollercoaster riding, jet skiing, rafting, bungee jumping, rappelling, paragliding, kayaking/canoeing, motor racing, snowboarding, BASE jumping and skydiving) before and after HCM diagnosis, along with major (ICD shock, syncope) or minor (nausea, dizziness, palpitations, chest pain) adverse events related to participation, and relevant physician advice.