My cardiac mri showed persistent left sided superior vena cava drains into a dilated coronary sinus w/ mild dilation of the main pulmonary artery?

Left SVC: Persistent left sided svc is not too rare. If persistent, it will drain into the coronary sinus. The coronary sinus will dilate and drain into the right atrium, like the normal right sided svc. The net result is the return venous blood flow still makes it to the right atrium either way. Wouldn't normally think of a dilation of the main pulmonary artery as typical with a persistent svc.

Mostly a normal: Variant. Every fetus has one, but in most it involutes before birth. 0.3% of the general population has one. It is the most common variation of the thoracic venous system. Left svc draining into coronary sinus is expected 90% of the time. Discuss with your doctor the significance in your case of the mild dilation of the pulmonary artery.