Abstract: Objective To explore the effects of decline of pH value on cardiomyocyte viability of rats, and to analyze the possible mechanism. Methods Hearts of five newborn Sprague-Dawley rats were isolated, and then primary cardiomyocytes were cultured and used in the following experiments. (1) The primary cardiomyocytes were divided into pH 7.4+ 6 h, pH 7.0+ 6 h, pH 6.5+ 6 h, pH 6.0+ 6 h, pH 6.5+ 1 h, and pH 6.5+ 3 h groups according to the random number table, with 4 wells in each group. After being routinely cultured for 48 h (similarly hereinafter), cells in pH 7.4+ 6 h, pH 7.0+ 6 h, pH 6.5+ 6 h, and pH 6.0+ 6 h groups were cultured with pH 7.4, pH 7.0, pH 6.5, and pH 6.0 DMEM-F12 medium (similarly hereinafter), respectively, and then they were cultured for 6 h. Cells in pH 6.5+ 1 h and pH 6.5+ 3 h groups were cultured with pH 6.5 medium, and then they were cultured for 1 h and 3 h, respectively. Viability of cells was detected by methyl-thiazolyl-tetrazolium (MTT) method. (2) The primary cardiomyocytes were divided into pH 7.4, pH 6.5, and pH 6.5+ taxol groups according to the random number table, with 2 wells in each group. Cells in pH 7.4 group were cultured with pH 7.4 medium, while cells in pH 6.5 and pH 6.5+ taxol groups were cultured with pH 6.5 medium. Cells in pH 6.5+ taxol group were added with taxol of a final molarity of 0.2 μmol/L in addition, and then they were cultured for 6 h. Morphology and density of microtubule of cells was detected by immunofluorescence assay. (3) The primary cardiomyocytes were grouped and treated as in experiment (2), with 2 wells in each group. The expressions of polymerized microtubulin and free microtubulin were determined with Western blotting. (4) The primary cardiomyocytes were grouped and treated as in experiment (2), with 4 wells in each group. Viability of cells after treated with taxol was detected by MTT method. Data were processed with one-way analysis of variance and LSD-t test. Results (1) The viability of cells in pH 7.4+ 6 h, pH 7.0+ 6 h, pH 6.5+ 6 h, pH 6.0+ 6 h, pH 6.5+ 1 h, and pH 6.5+ 3 h groups were 1.00±0.08, 0.90±0.08, 0.85±0.06, 0.83±0.04, 0.91±0.10, and 0.89±0.10, respectively. Compared with that in pH 7.4+ 6 h group, viability of cells in pH 7.0+ 6 h, pH 6.5+ 6 h, pH 6.0+ 6 h, pH 6.5+ 1 h, and pH 6.5+ 3 h groups were all decreased in different degrees (t=2.476, 4.002, 4.996, 2.168, 2.400, P<0.05). (2) Microtubules of cells in pH 7.4 group were radially distributed around the nucleus with clear tubular structure. Compared with that in pH 7.4 group, the skeleton of microtubules of cells in pH 6.5 group was obviously damaged, with broken structure of microtubule and reduced density. Compared with that in pH 6.5 group, the damage degree of microtubules of cells in pH 6.5+ taxol group was obviously alleviated, and the structure of microtubules basically returned to normal. (3) Compared with that in pH 7.4 group, the expression of free microtubulin of cells in pH 6.5 group was significantly increased (t=3.030, P<0.05), while the expression of polymerized microtubulin of cells was significantly decreased (t=8.604, P<0.05). Compared with that in pH 6.5 group, the expression of free microtubulin of cells in pH 6.5+ taxol group was significantly decreased (t=4.559, P<0.05), while the expression of polymerized microtubulin of cells was significantly increased (t=5.472, P<0.05). (4) Viability of cells in pH 7.4, pH 6.5, and pH 6.5+ taxol groups were 1.00±0.10, 0.83±0.04, and 0.93±0.10, respectively. Compared with that in pH 7.4 group, the viability of cells in pH 6.5 group was obviously declined (t=4.412, P<0.05). Compared with that in pH 6.5 group, the viability of cells in pH 6.5+ taxol group was obviously increased (t=2.461, P<0.05). Conclusions The decline of pH value reduces the viability of cardiomyocytes of rats through destroying the skeleton of microtubule. Stabilizing microtubule skeleton can significantly reduce acidic treatment-induced damage and ameliorate cardiomyocyte viability.