There are numerous toxins and drugs that can cause, in overdose, ECG changes, even in patients without history of cardiac pathology. Theophylline intoxication results in substantial morbidity and mortality, particularly in those with chronic overmedication. The aim of this work was to study ECG changes in cases of poisoning by theophylline overdose that were admitted to MPCC over 2011 and the relation between ECG changes, theophylline blood level and poison severity score. In this study, theophylline overdose patients admitted to MPCC in the period from 1^st of January 2011 to 31^st of December 2011 were included. The total patients' number was 44 patients. Most cases of the study were females (77.2%) in the age group of (20-<40) years (40.9%), mainly from rural side (65.9%). Regarding relation between theophylline serum level and clinical manifestations, a significant relation was found between serum level and each of vomiting and dizziness, where both were noticed with majority of cases of minimal and moderate toxicity serum level. Regarding poison severity score, exactly one half of moderate and severe cases had minimal toxicity serum level, and the other half had moderate toxicity level. A significant negative correlation between theophylline serum level and PCO₂ was found. There was a non significant negative correlation between theophylline serum level and each of Na and K blood level. Concerning ECG changes, a significant relation was found between theophylline serum level and each of sinus tachycardia and second degree heart block.