The answer is all 3. GP for the small stuff, kidney for the renal problems
, and cardiologist for the heart
At home he should be drastically limiting salt(sodium), or anything with salt(sodium) added. He should try to stay with fresh meat, vegetables, and fruits, with low sodium breads. EVERYTHING he consumes needs to be low/no sodium.
If he finds himself thristy a lot of the time, he could suck on crushed ice. It seems to work better than plain water for quenching thirst.