Answer:
Endocarditis
Explanation:
Endocarditis is a condition developed by the infection of the inner layer of the heart called endocardium.
The person suffering from the endocarditis develop symptoms suddenly or very slowly depending on the micro-organism that could be the cause of the endocarditis.
It is impossible for the doctor to tell the exact cause of the endocarditis which leads to the damage of the heart valves.
Thus, Endocarditis is the correct answer.
