The two things could very well be possibly connected. There are many causes of pericardial effusion. Basically, your heart is surrounded by a sac, with some fluid which helps prevent friction from the heart rubbing against other organs etc, and helps protect the heart. An effusion means there is more than the usual amount of fluid present. Although trivial, your cardiologist will have to find the cause and treat you. Trivial also means you won't need to have it drained, the body will normally reabsorb that excess. One thing which can cause pericardial effusion is an infection, bacterial or fungal. So the right antiobiotics are essential. This infection could also be the cause of the thickening leaflets on your mitral valve.
If infection is the cause, it looks like it has been caught nice and early before any serious damage is done.