what can I say ? uhm....

the best thing that happened to me..

Owner of my heart..

Ne söyleyebilirim? uhm....

En iyi birþey bana geldiði ..

Kalbimin sahibi ...

Please wait for corrections, just a learner.

Ne diyebilirim?

Baþýma gelen en iyi þey..

Yüreðimin sahibi.

which one is the most informal?

Well, I think Impulse is a native speaker and Melek74 I know is not.  Kalp means the heart organ in the the body as as well as the ´feeling´ heart.   Yürek is more like emotions only.  I would say the second attempt is more informal the way you probably mean.

I agree, Impulse´s translation is I´m sure better as he´s a native speaker and I´m just learning. I´m just wondering about the kalp vs. yürek distinction. I´ve seen kalp used in some songs, like "Sorma Kalbim" or used in the expression "kalbimdesin" (you´re in my heart), so I´m wondering if there´s a rule of thumb where one should be used over another.

Kalp and yürek has the same meaning of heart organ. And also have the meaning of heart, soul and willingness.

But also they have different meaning:

Kalp has the meaning of love and desire. But yürek has the meaning of courage and bravery.

Kalp has the meaning of feeling and yürek has the meaning of mercy.

I think, because kalp´s meanigns mostly towards "love", they use it occasionally in songs and poems.

 Thanks Faruk!

 Thank you Faruk for the explanation , I wish they put that in the dictionaries too .