The coronary arteries arise from the ascending aorta and form a circulatory loop around the heart. The right coronary artery originates from the right sinus and supplies the right atrium and ventricle. The left coronary artery originates from the left sinus and divides into the left anterior descending artery and circumflex artery to supply the left side of the heart. Blood from the heart drains primarily into the coronary sinus which empties into the right atrium.