Circumflex artery, which passes behind the heart between the left atrium and left ventricle and supplies blood to the side (lateral wall) of the left ventricle. In a small number of people, the circumflex artery supplies the lower and back portions of the left ventricle. The right coronary artery supplies blood to the right ventricle and then supplies the underside (inferior wall) and backside (posterior wall) of the left ventricle. What are collateral coronary arteries?