I hadn't heard about the endothelium until a year or so ago. It doesn't sound like something that's terribly interesting which is a shame because it does appear that if we understood what it does then we could devise better strategies for the prevention of heart disease and management of existing conditions. Wow, that was a mouthful!
It also appears that a proper, regular exercise plan will be beneficial. No surprise there then. Here's a link which you may find useful.
http://www.patient.co.uk/doctor/Heart-Disease-and-Exercise.htm