Heart : Cardiology :: kidney : ?

Cardiology - the study and treatment of medical conditions of the heart.

Nephrology - the area of science and medicine that is concerned with the kidneys.

Urology - the area of medicine concerned with the parts of the body that produce and carry urine.

Ophthalmology - the scientific study of eyes and their diseases.

Cytology - the scientific study of cells from living things.

অর্থাৎ, heart এর রোগ সম্পর্কিত বিদ্যা হচ্ছে - Cardiology এবং kidneys এর রোগ সম্পর্কিত বিদ্যা হচ্ছে - Nephrology