This is a literal translation, and it is a fairly common way to express the sentiment. However, you could also use other phrases depending on the context, such as:
* Yn fy nghalon - This is a more direct and simple translation, meaning "in my heart"
* Yn fy mherthynas - This means "in my relationship", and could be used to convey the sentiment of feeling something strongly about someone or something
* Yn fy meddwl - This means "in my mind" or "in my thoughts" and could be used to express a more intellectual or emotional connection
Ultimately, the best translation for "in my heart" will depend on the specific context of your sentence.