My 3yr old son has had a PDA closure and also has a coronary fisula. Je sweats profusely at night how can I help?

Get Checked. The history of a coronary fistula should lead us to be cautious. However, sweating when sleeping would not be a common way in which a problem showed itself. Rather, sweating with activity would be more concerning. Nevertheless, please bring this up with the cardiologist and pediatrician. You should rule out any residual heart issue and remember that it may be unrelated as well.
See below. This problem can only be solved by seeing his doctor and being evaluated face-to-face. After a thorough examination, his doctor should be able to tell you what's wrong and what to do about it.