I think knees are a big problem in malll dogs, luxating patellas???
I might wonder what is causing marty's bronchitis - does he have a thread here?
I think joint products, particularly with hyaluronic acid can help keep the tendons of the heart supple. My 1st girl had mitral valve disease and a broken tendon in her heart - if caught in time, it can be managed, which is the good news.
Worried that we haven't heard back from the OP