Please capitalize where necessary: mitral and tricuspid valve heart failure
A: Mitral and tricuspid valve heart failure

Please capitalize where necessary: the flu virus is highly contagious, especially through the winter months. to protect against influenza, you can obtain the flu...
A: The flu virus is highly contagious, especially through the winter months. To protect against influenza, you can obtain the flu...

Please capitalize where necessary: the following would be a good example:
A: The following would be a good example:

Please capitalize where necessary: the area, also known as polesie (belarusians - their own, we have - his own, all to be honest ), it was formed in december 1939.
A:
The area, also known as Polesie (Belarusians - their own, we have - his own, all to be honest ), It was formed in December 1939.