Background: Type 1 diabetes (T1DM) patients suffer from a variety of pathological insults that affect the heart including accelerated atherosclerosis, cardiac autonomic neuropathy and possibly intrinsic diabetic cardiomyopathy (DC). Diastolic dysfunction is often the first manifestation of DC preceding the systolic damage and clinical signs of heart failure. Diastolic dysfunction has an increased value of P-wave dispersion (PD) which is described as an indicator for diagnosis of atrial arrhythmia. Aim: To show the effect of chronic hyperglycemia in type 1 diabetic children on PD and diastolic function and to correlate the results with glycemic control, diabetes duration and complications. Subjects and Methods: Cross-sectional, case-control, prospective study included 50 children with T1DM attending the outpatient DEMPU clinics and 30 healthy controls. Glycosylated hemoglobin (HbA1c), lipid profile, albumin/ creatinine ratio, cardio-autonomic reflexes, conventional 12 leads electrocardiography (ECG), and Echocardiography were evaluated. Results: HbA1C, total, cholesterol, and LDL were found significantly higher in diabetic patients than in controls with a P-values of (0.0001 for each). As regards echocardiographic data and p-wave characteristics; E mitral, E/A ratio, E tricuspid, and A tricuspid were found significantly higher in control group than T1DM patients with a P-value of (0.0001for each), while IVRT, LVEDD, IVRTTR, and PD were found significantly higher in diabetic patients compared to the control group with a P-value of (0.0001, 0.0001, 0.04, and 0.005 respectively). Significant positive correlation was found between PD and LVEDD (r=0.3, p-value=0.04). Significant negative correlation was found between PD and both of A mitral, and IVRT (r=-0.32, p-value=0.03, and r=-0.38, p-value=0.01 respectively). Significant negative correlation was found between postural fall in blood pressure and E/A tricuspid (r=-0.34, p-value=0.02). Significant positive correlation was found between the LDL level and the alb/creat ratio (r=0.32, p-value=0.02). Significant negative correlation was found between the duration of the disease and E mitral and E/A ratio mitral (r=-0.38, p-value=0.01, and r=-0.29, p-value=0.04 respectively). Significant positive correlation was found between the duration of the disease and IVRT (r=0.39, p-value=0.0001). Conclusions and Recommendations: An alteration of myocardial function induced by DM may begin earlier than generally thought, and these changes are accelerated when glycemic control is poor. Early institution of close observation of T1DM patients for alterations in cardiac function is highly recommended. Also, vigorous treatment of micro-albuminuria may improve lipid profile as well as the kidney and the heart.