Exposure to ambient air pollution is consistently associated with increased cardiovascular morbidity and mortality; however, the underlying pathophysiologic mechanisms remain unclear. High left ventricular voltage has been related to cardiac dysfunction.Therefore, this study aimed to investigate the association between longitudinal exposure to size-fractioned particulate matter (PM) and left ventricular voltage (assessed as the sum of the voltages of the R-wave in lead V5 [RV5] and S-wave in lead V1[SV1]) among 88 healthy, young Chinese adults. We collected weekly 12-lead electrocardiogram (ECG) and serum biomarkers from each participant five times over 35 days. The fixed point, real-time, mass concentrations of particles with aerodynamic diameters of ≤2.5 μm (PM_2.5), PM₁, PM_0.5, and number concentrations of particles with aerodynamic diameters of ≤0.2 μm (PNC_0.2), PNC_0.1, and PNC_0.03 were monitored in the catchment area, and linear mixed-effect models were used to estimate the associations between the size-fractioned PM exposure and ECG indices. The results showed that there was a significant association between higher size-fractioned PM levels and higher RV5+SV1 voltage within 24 h of exposure. We detected increases in the RV5+SV1 voltage of 0.060, 0.058, 0.090, 0.084, and 0.077 mV per interquartile range (IQR) PM_2.5 (45.92 μg/m³; 95% confidence interval [CI] = 0.003, 0.117), PM₁ (43.51 μg/m³; 95% CI = 0.003, 0.113), PNC_0.2 (14.92 × 10³ particles/cm³; 95% CI = 0.017, 0.163), PNC_0.1 (12.79 × 10³ particles/cm³; 95% CI = 0.004, 0.163), and PNC_0.03 (5.43 × 10³ particles/cm³; 95% CI = 0, 0.153), respectively. The associations between the RV5+SV1 voltage and size-fractioned PM exposure were stronger among participants with greater serum concentrations of monocyte chemoattractant protein-1, soluble CD40 ligand, plasminogen activator inhibitor-1, and total cholesterol, and lower high-density lipoprotein cholesterol levels. Exposure to various PM size fractions (PNC_0.03-PNC_0.2, and PM_0.5-PM_2.5) may increase the left ventricular voltage among healthy young adults, and the effects may be modified by inflammation, coagulation, and lipid biomarkers.