The mitogen-activated protein kinase (MAPK) p38 signaling pathway is essential for normal heart function. However, p38 also contributes to heart failure pathogenesis by affecting heart contractility and cardiomyocyte survival. To unravel the complex cardiac role of p38, we report the interactome of p38α and p38γ, the two well expressed isoforms in the heart, obtained via an APEX proximity assay performed in cultured neonatal rat ventricular myocytes. The p38α and p38γ have distinct interactomes in cardiomyocytes for both studied states; basal and activated by an osmotic stress. Interestingly, the activated p38α interactome contains many spliceosome implicated RNA-binding proteins. The serine/arginine-rich splicing factor 3 (SRSF3) is of particular interest and its interaction with p38α was validated by co-immunoprecipitation. p38 is sufficient to partially relocate nuclear SRSF3 to cytoplasm. The alternative splicing function of SRSF3 is also modulated by the p38 pathway. Our findings reveal a novel set of proteins to investigate in order to decipher cardiac functions of the MAPK p38, as well as a specific regulation mechanism of SRSF3 by p38 in cardiomyocytes.