The lesion shown in the histopathological slide is Aschoff's body and the most probable diagnosis is rheumatic heart disease (RHD).
Aschoff's bodies are the lesions found in the heart during acute rheumatic fever.
They are composed of foci of T lymphocytes, activated macrophages called Anitschkow cells, and occasional plasma cells.
Anitschkow cells have abundant cytoplasm and central round-to-ovoid nuclei with chromatin that is centrally condensed into a slender, wavy ribbon.
Hence, they are also called caterpillar cells.
Rheumatic fever is the leading cause of mitral stenosis. During acute rheumatic fever, Aschoff bodies may be found in any of the three layers of the heart that results in pericarditis, myocarditis, or endocarditis.
Chronic inflammation leads to diffuse thickening and fibrosis of the valve leaflets, often with calcific deposits.
Fibrinoid necrosis occurs due to inflammation of the endocardium and the left-sided valves.
Over these areas of necrosis, small vegetations called verrucae develop along the lines of closure.
Irregular thickenings present in the subendocardium are called MacCallum plaques.
In chronic RHD, the mitral valve leaflet is thickened, with commissural fusion and shortening.
There is thickening and fusion of the tendinous cords.
This can lead to narrowing the mitral orifice, leading to a fish mouth appearance (button hole).
Some major manifestations of rheumatic Fever are:

Other Options:

Option B: Degenerative calcific deposits in the mitral valve typically develop in the fibrous annulus. They are seen grossly as irregular, stony hard, occasionally ulcerated nodules at the base of the leaflets. Usually, it does not affect valvular function. However, occasionally it can lead to regurgitation, stenosis, or arrhythmias.
Option C: In sarcoidosis, the involved tissues contain well-formed non-necrotizing granulomas. They are composed of aggregates of tightly clustered epithelioid macrophages, often with giant cells, usually without central necrosis. As the lesions become chronic, fibrous rims or hyaline fibrous scars enclose the granulomas.
Option D: In tuberculosis, sites of active involvement of tuberculosis are marked histologically by a characteristic granulomatous inflammatory reaction composed of both caseating and non-caseating tubercles. Usually, granuloma shows central granular caseation surrounded by multinucleate giant cells. Central caseation may be absent in non-caseating granulomas. Staining should be done to detect acid-fast bacilli when granulomas are present.

Reference: Harrison's Principles of Internal Medicine 20th Edition (Page no:1814, 254, 2543).

Cardiovascular Pathology