Heavy loads of tartar / calculus lead to periodontal disease. This is when the gums and tooth attachments are damaged due to infection of the tissues.
But these bacteria can spread around the whole body through the blood stream causing widespread organ problems. The kidneys, heart, lungs and liver are most commonly affected causing renal failure, endocarditis, pneumonia and hepatitis. These changes may be picked up on pre-anaesthetic blood tests, but more tests may be required to identify the severity of the problem.
Dealing with the periodontal disease will often allow these systemic problems to improve but it is better to prevent it happening in the first place.
Regular dental check-ups will identify dental disease early and allow appropriate treatment to begin before these problems can cause life threatening complications.