Introduction: Pulmonary arterial hypertension (PAH) is a lethal syndrome characterized by pulmonary vascular obstruction that is partially due to hyperproliferation of apoptosis-resistant pulmonary arterial smooth muscle cells (PASMC). This “pseudoneoplastic phenotype” of PAH PASMC is due, in part, to excessive mitochondrial fission caused by activation of dynamin related protein-1 (Drp-1) and its binding partner MiD49. The mechanism by which MiD49 regulates the proliferation of PASMC is not completely understood. Here we investigate the possibility that MiD49 promotes cellular proliferation by regulating a non-filamentaous class-1 myosin protein, MYO1C. Hypothesis: MiD49 regulates cell proliferation via a MYO1C-dependent mechanism, which is pathologically upregulated in PAH. Methods: MiD49 and MYO1C expression was compared between normal (n=4) vs PAH (n=5) human PASMC using western blot analysis. The colocalization was visualized using super-resolution confocal microscopy. The effects of manipulating MYO1C on cell proliferation and apoptosis were assessed by flowcytometry. Results: MiD49 and MYO1C are upregulated and colocalized in PAH PASMC. The expression of MYO1C positively correlated with MiD49 in PAH. Silencing MiD49 downregulated MYO1C expression whilst augmenting MiD49 upregulated MYO1C. Silencing MYO1C, however, does not affect MiD49 expression, proving that MYO1C is downstream of MiD49. The downregulation of MYO1C by MiD49 silencing is rescued by a proteasomal blockade, MG132. Downregulating MYO1C using siRNA inhibited proliferation, prevented ERK1/2 activation, and induced apoptosis in PAH PASMC. Conclusion: Increased proliferation and apoptosis resistance of PAH PASMC are in part due to the dysregulation of MiD49-MYO1C pathway. Targeting this pathway may have therapeutic implications against PAH.