Abstract: AIM To explore the hypertropic effect of different concentrations of rat parathyroid hormone1-34 (rPTH1-34) in ventricular cardiomyocytes in vitro and to investigate the changes of extracellular signal regulated kinases 1/2 (ERK1/2). METHODS Hypertrophy in neonatal rat cadiomyocytes was induced by 1×10-8～1×10-6 mol/L rPTH1-34 in 24 h in vitro. Cellular diameter, 3H-Leucine incorporation and mRNA expression of atrial natriuretic peptide (ANP) were detected, and protein expression of ERK1/2 and phospho-ERK1/2 (p-ERK1/2) was measured. RESULTS Compared with that in normal control group, 1×10-8 mol/L rPTH1-34 slightly increased single cellular diameter, the synthetic rate of protein and mRNA expression of ANP but with no statistical significance. Both 1×10-7 and 1×10-6 mol/L rPTH1-34 markedly increased single cellular diameter (P<0.01), the synthetic rate of protein (P<0.01) and mRNA expression of ANP (P<0.01). Compared with that in normal control group, PTH increased protein expression of ERK1/2 and p-ERK1/2 in a concentration-depended manner (P<0.01). CONCLUSION 1×10-7 and 1×10-6 mol/L rPTH 1-34 induce hypertrophy in neonatal rat cadiomyocytes in vitro in a concentration dependent manner. PTH leads to the over-expression of ERK1/2 in a concentration-dependent manner.