I have a Sorin mechanical valve and this is MRI safe. I have found some information on MRI compatibility on their website and the temperature may rise about 1.5 degrees in a 3T MRI scanner (if I remember correctly). This information is only talking about temperature increase. It is the RF that will heat you up. My mechanical valve is made out of titanium and carbon, which is fully MRI safe. All tooling we use in our MRI business is made out of titanium.
I work in MRI business and I am frequently in the magnetic field (1.5T and 3.0T scanners) without any problems. However, since I have my mechanical valve, I have never been in an MRI to have some scans made. Only working in the static magnetic field, which is no issue for the mechanical valve.