I believe endocarditis and strep are both bacterial, not viral, so not sure how to relate those to covid-19.
It's hard to find specific information, but what I have put together from listening to several interviews is the main problems are age, obesity, diabetes, hypertension, and weak immune system, not necessarily in that order. I think some people with heart disease are high risk and others not as much. I don't believe an artificial valve alone is a significant risk, if your heart is otherwise healthy. I had a pulmonary test as part of workup for valve replacement and my lungs were in excellent shape. If someone has a pulmonary deficiency along with an artificial valve, then they are likely at higher risk.
Early on, there were reports of coronavirus attacking the heart (ace-2), but I haven't seen any recent reports verifying that. It appears the virus attacks the lower respiratory system, which is why so many need to be on ventilators. How is your health leaving out the heart valve? I think that is the important question.
I am disappointed the task force hasn't published health information on people who have had critical cases or died from covid-19. The best we can do is try to not get covid-19. CDC should have been more specific about who are at risk and recommended everyone wear a mask at least a month ago.
ETA: One other interesting tidbit I picked up is that the majority of old people have at least 1 co-morbidity. So when they say over 65 (or whatever age they use) with co-morbidity, that includes most people over 65.