Diuretics

Commonly used cardiac drugs. They get rid of water and used in oedema (reduces excess water) and hypertension (reduces fluid and thus pressure in circulation).

Loop

Furosemide acts on a Na-K symporter (kicks out K⁺, reabsorbs Na⁺). Thus hypokalaemia is a side-effect

Thiazide

Bendroflumethiazide prevents Na⁺ reabsorption. Thus hyponatraemia is a side-effect.

Potassium-sparing

Spironolactone. Seems to be pretty awesome. Gains K⁺ so hyperkalaemia is a potential side-effect. Probably expensive or something.