ECG at rest (A), peak exercise (B), and during recovery (C). ECG was recorded at 25 mm/s, 20 mm/mV, and 60 Hz. ST elevation is apparent in leads V1-V3 with exercise, and is most prominent in V3 (B and C). In lead II, the height of the P wave becomes more prominent during exercise and persists into recovery (B and C). Note the deeper S-wave in leads V5 and V6 at peak stress (B) and in leads V5 and lead I during the recovery phase (C).