<prompt> Vein opening directly into right atrium:Anterior cardiac veinMiddle cardiac veinGreat cardiac veinSmall cardiac vein  <response>: Anterior cardiac veinThe anterior cardiac veins or anterior veins of right ventricle, comprising three or four small vessels which collect blood from the front of the right ventricle and open into the right atrium.Unlike most cardiac veins, it does not end in the coronary sinus.Instead, these veins drain directly into the anterior wall of the right atrium. 