Dialysis patients have higher rates of sudden cardiac death. The study of the electrocardiogram could identify patients at risk of developing rhythm disorders. The aim of this study was to evaluate the electrocardiographic findings before and after the hemodialysis (HD) session and to examine associations of clinical and serum electrolytes with electrocardiogram findings. We conducted a multicentric transversal study, including chronic HD patients during January 2018. Standard 12-lead electrocardiogram was recorded, before and after the HD session. A medical history was documented. It included age, gender, initial nephropathy, and comorbidities. Serum potassium and total serum calcium were measured before a routine HD session. Serum potassium was measured after HD session. Corrected QT for heart rate was calculated using Bazett's formula. The study included 66 patients. Nineteen patients (28.8%) had hyperkalemia before the HD session and 44 (66.7%) patients had hypokalemia after the HD session. Seventeen patients had prolonged QTc interval (25.7%). On multiple regression analysis, only the prolonged QTc interval was significantly correlated with the serum potassium (P = 0.046).When comparing the mean values of electrocardiogram parameters before and after the HD session, we noted a significant change of heart rate (P = 0.001), R wave (P = 0.016), T wave (P = 0.001), and T/R (P = 0.001) wave. Delta K+ did not correlate with the change in T wave amplitude (r = 0.23, P = 0.59), R wave amplitude (r = -0.16, P = 0.2), T/R wave (r = 0.055, P = 0.65), or QRS duration (r = 0.023, P = 0.85). Delta QTc was correlated to ΔK+. We conclude that usual electrographic manifestations of hyperkalemia are less pronounced in HD patients. Our results confirmed the unstable status of cardiac electrophysiology during HD session.