The biggest functional issue with a pericardial effusion is that the fluid can create a kind of compressive phenomenon, where the heart cannot fill properly because space within the pericardial sac is being occupied by the effusion. This means that, to get the same cardiac output, you have to run a much higher pulse rate, and that's hard work for the heart.
It isn't always true; if the effusion has accumulated slowly and the pericardium (which is not very elastic) has slowly stretched, you can have a huge cardiac silhouette on chest x-ray, and a normal-sized heart within it.
But DDM is entirely correct; the focus right now should be on diagnosing WHY you have a pericardial effusion, and what, if any effect it is having on your cardiac performance. Effusions are neither normal nor common, and a wide variety of conditions can cause them. It's important to figure out what is doing this, because there are effective treatments for some of the causes.