Patients presenting with acute pericarditis demonstrate diffuse ST segment elevation in all leads except aVR and V1 (see below). These ST changes are sometimes associated with concurrent PR segment depression in the same leads and an increased sinus heart rate (above 138 bpm). At 2-5 days after the acute presentation, the ST segments return to baseline. Following this return to baseline, the T waves in all leads except aVR become inverted, eventually returning to their previously normal polarity and amplitude over the following couple of weeks.