Objective The purpose of our study is to observe the voltage-gated potassium channel Kv1.3 expressed on CD4+CD28null T cells from the peripheral blood of acute coronary syndrome (ACS) patients by the patch clamp technique. Methods Kv1.3 potassium channels expression from 17 patients with ACS and 11 healthy age-match controls was detected in single cell(CD4+CD28null T cells and CD4+CD28+T cells) by fluorescence microscopy and patch clamp. Results The percentage of CD4+CD28null T cells was higher in the ACS patients [(6.97±2.05)%] than that in the controls [(1.38±0.84)%, P<0.05]. The concentration of hsCRP was directly correlated with the number of the CD4+CD28null T cells in the ACS patients (r=0.52, P<0.05). The conductance (6.89±1.17ns vs 3.36±0.66ns), dens (1.95±0.80μm2 vs 1.13±0.57μm2) and numbers (574.5±97.6 n/cell vs. 280.3±55.3 n/cell) of the Kv1.3 channels on the CD4+CD28null T cells were significantly higher than those on the CD4+CD28+ T cells (all P<0.01) in ACS patients, but were similar on CD4+CD28+T between ACS patients and controls. Conclusion The CD4+CD28null T cells and the numbers of Kv1.3 channels on the CD4+CD28null T cells from patients with ACS are significantly upregulated and might contribute to the pathogenesis of ACS.