Yes. Heart surgery is definitely major surgery. It requires the coordinated effort of several doctors, nurses, and technicians. Often the patient is placed on the heart lung machine and the heart is stopped temporarily. The arteries on the heart are usually only 1-2 mm in size - the size of a wire in a paper clip. Fortunately the rate of complication is very small.
Yes. Yes, any open heart surgery is serious and complicated to do, but thousands are done every day in th us with only a 1 to 2 percent mortality.