Vegetations on under-surface of A. V. valves are found in:

Vegetations occur on the surfaces of the cusps in libman sacks endocarditis and infective endocarditis. Both surfaces may be involved in both the disease but undersurface is more commonly seen in libman sacks endocaritis. Ref: Robbins Pathologic Basis of Disease By Stanley Leonard Robbins, Ramzi Coan, 7th Edition, Page 597