During an xray what causes widening of vessels around the heart?

Various causes: Engorgement is due to volume overload as from congestive heart failure or renal failure. Focal enlargement of a vessel may indicated an aneurysm. Widening of the mediastinum can indicate aortic dissection. Central pulmonary artery prominence can be due to pulmonary hypertension. Poor x-ray technique can cause magnification that is artifactual. I'm not a radiologist but that's a quick answer.