Autopsy and echocardiographic studies indicate that ECG criteria for LVH tend to maintain their sensitivity in the presence of LBBB, with the exception of left precordial lead criteria alone. With RBBB, ECG criteria for LVH using right precordial S waves and combination criteria of right precordial S waves and left precordial R waves have a marked reduction in sensitivity, whereas left precordial R wave criteria have modestly reduced sensitivity. Limb lead criteria for LVH have increased sensitivity in the presence of RBBB and, to a lesser extent, in the presence of LBBB. Acceptable sensitivity for the diagnosis of LVH in patients with bundle branch block requires a combination of limb and precordial lead voltage criteria and/or other nonvoltage ECG criteria, since the prevalence of LVH in the presence of RBBB or LBBB appears higher than the sensitivity of individual criteria.