Greater than how many millimeters does the ST segment have to be to be indicative of a heart attack Solution An ST elevation is taken into consideration elevated if the vertical distance within the ECG and the baseline at a point 0.24 seconds after the J-factor is at least 0.9 mV (commonly representing 1 mm ) in a limb lead or 0.29 mV (2mm) in a precordial lead Hope you understand....