Important clarification: symptoms typically resolved within weeks, while echocardiographic findings are what may persisit for up to a year. Both UW and AMBOSS confirm.
UW Step 2 - 20421: "HCM in these patients is transient as insulin levels normalize in the first few weeks of life, and medical management is rarely required beyond the neonatal period. Spontaneous regression of echocardiographic findings occurs by age 1"
Source: AMBOSS - https://next.amboss.com/us/article/Rs0luh?utm_source=amboss-anki-deck-template-script&utm_medium=anki&utm_campaign=amboss-anki-deck-template-script-beta&utm_term=transient+hypertrophic+cardiomyopathy&aid=298bfc66-b119-4c76-b7ef-8bfc7d192ab2&uid=ptfeLeLy0#Z5c2a717019332d9becba8e0a04c27104