BLOOD OXYGEN SATURATION DETERMINATION

A medical implant device can comprise a light source and a light sensor, and a housing configured to receive the light source and the light sensor. The housing can comprise a first wall portion configured to be positioned over an extraluminal surface of a coronary sinus, the first wall portion comprising a first surface oriented toward the extraluminal surface. A first light-transparent region of the first wall portion can be configured to allow passage therethrough of an emitted light signal from the light source into the coronary sinus, and a second light-transparent region of the first wall portion can be configured to allow passage therethrough of a reflected light signal from within the coronary sinus for detection by the light sensor.