Plankton is not the name of a plant or animal but more of a category for any drifting organism that inhabits the middle to upper levels of the ocean, namely the pelagic zone.
Most vets do spays, neuters, bone surgeries, spleen surgery, tumor removals, and intestinal surgeries. Heart surgery and more complicated surgeries are done by specialists that requires more schooling. If you want to be a vet, you have to have REALLY good grades and Vet school is MUCH harder to get into than human medical school.
Interventional Cardiologists - treat patients who are dealing with coronary artery disease, heart valve disease, and peripheral vascular disease. They do angioplasty and stent placements, embolic protection, atherectomy procedures, and mitral valve repairs.