All veins opens into coronary sinus, EXCEPT:

The coronary sinus drains all the venous blood of the hea, except those carried by anterior cardiac veins and venae cordis minimae. Anterior cardiac veins opens into the right atrium, to the left of the opening of inferior vena cava. Venae cordis minimae drain directly into the chambers of the hea. The coronary sinus receives the following veins: (1) the great cardiac vein; (2) the small cardiac vein; (3) the middle cardiac vein; (4) the posterior vein of the left ventricle; and (5) the oblique vein of the left atrium.