If you want to understand inside heart anatomy!

https://www.frontiersin.org/articles/10.3389/fcvm.2018.00080/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_702197_103_Cardio_20180712_arts_A

Figure 1. Comparison of the atrial septal surfaces. (A). The septal surface of the left atrium is characterized by the flap valve of the fossa ovalis (septum primum), in contrast to the limbus of the fossa ovalis (*) present on the right atrioseptal surface (B). The source of light indicates the fossa ovalis, the blue band depicts the position of the aortic non-coronary sinus. LA, left atrium; MV, mitral valve; SP. septum primum; IVC, inferior vena cava; RA, right atrium; RAA, right atrial appendage.