The present invention relates to an atrial retractor (1) for retracting the incision and for supporting cardiac tissue (104) of the atrial ceiling during surgery on a mitral or tricuspid valve. The foldable retractor comprises a tubular retractor body (2) with a central opening (3), a proximal flange (8) and a distal flange (12). The distal flange (12) is dome segment-shaped or spherical crown-shaped to support, once the retractor has been delivered in the incision (101), the round shape of the bloodless atrial ceiling (40), which tends to collapse.