The presence or onset of bundle branch block (BBB) is associated with increased mortality in patients after acute myocardial infarction (AMI). The risk increases with age. We assessed the prognostic power of BBB patterns for predicting clinical outcomes in patients after high-risk AMI. In the OPTIMAAL trial, the effects of losartan versus captopril were compared in 5,477 patients with heart failure and/or evidence of left ventricular dysfunction after MI. The association between clinical outcomes and the presence of left or right BBB at randomization (median 3 days after AMI) or occurring during follow-up (mean 2.7 years) was assessed using Cox regression models. At randomization, 8% of patients (n = 438) showed BBB patterns; 3.7% (n = 203) showed left BBB and 4.3% (n = 235) showed right BBB patterns. In patients with left BBB, there was an increased risk of all-cause death and cardiovascular death. In patients with right BBB, there was increased risk of sudden cardiac death/resuscitated cardiac arrest. During follow-up, another 4.9% (n = 272) developed BBB patterns; 2.8% (n = 153) developed left BBB and 2.17% (n = 119) developed right BBB. Left BBB was associated with increased risk for all-cause death, cardiovascular death, and sudden cardiac death/resuscitated cardiac arrest, whereas right BBB was related to increased risk of sudden cardiac death/resuscitated cardiac arrest. In conclusion, our results confirm and quantify previous observations showing substantially increased mortality in patients with BBB patterns at baseline or occurring soon after AMI.