Definition: Anastomosis is a surgical procedure involving the joining together of two or more tissues, organs, or vessels, typically during surgery. It's used to connect diseased or malfunctioning tissue pieces or tubes to heal properly. The key difference between anastomotic and pericardial anastomosis (the removal of the left side of the aorta in heart surgery) is that the right side remains open as the body heals, while the left side is sealed by stitches. This technique helps prevent blood clots from forming around the opening.