The therapeutic application of cell therapy to repair the damaged heart requires a comprehensive understanding of the process of cardiac differentiation of stem cells. We discovered a cardiac-specific marker, lysophosphatidic acid receptor 4 (LPAR4), which is G protein-coupled receptor (GPCR) and demonstrated its functional significance during cardiac differentiation. We screened GPCR expressing on mouse cardiac progenitor cells at differentiation day 3 compared to mouse undifferentiated pluripotent stem cells (PSCs). Among candidates, we identified LPAR4. We have found that in both mouse and human PSCs, LPAR4 has a transient expression pattern during cardiac differentiation. During in vitro differentiation of mouse and human PSCs toward cardiomyocytes, LPAR4 expression peaked for 3-5 days and then and declined immediately. Treatment with ODP (LPAR4 specific agonist) followed by p38MAPK blocker (SB203580) in the cardiac differentiation protocol significantly increased cardiac differentiation efficiency. Then we performed RNA sequencing to find transcription factors that regulate LPAR4. We screened 2-fold up-regulated transcription factors that related to cardiac differentiation during human iPSCs toward cardiomyocytes. The expression of LPAR4 is regulated by SOX17 expression, demonstrating that SOX17 is an upstream regulator of LPAR4. During cardiac differentiation, when knocking down SOX17 by siRNA, the expression of LPAR4 decreased as the expression of SOX17 mRNA decreased, resulting in no progression of cardiac differentiation. Besides, cardiac differentiation did not progress when SOX17 was overexpressed. SOX17 plays a role early in cardiac differentiation and that the expression should be reduced. However, it is assumed that sox17 lentivirus was gene-integrated and continued expression without decreasing expression. SOX17 overexpression needs further study. In conclusion, we demonstrated that LPAR4 is a novel cardiac progenitor cell marker and modulation of the upstream and downstream regulators shown functional significance during cardiac differentiation. Furthermore, our findings provide new insight into cell-free cardiac repair by the modulation of LPAR4 positive cells in the heart. Funding Source: This study was supported by "Strategic Center of Cell and Bio Therapy for Heart, Diabetes & Cancer" (HI17C2085) through the Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, Republic of Korea.