The Selvester QRS scoring system has previously been shown to enable estimation of myocardial infarct (MI) size by quantitative evaluation of the 12-lead ECG. The aim of this study was to assess the system's ability to detect and quantify lateral MI, using cardiac magnetic resonance (CMR) as reference standard.In 23 patients with isolated lateral infarctions MI size was assessed by CMR and estimated by QRS scoring. The ECGs were also evaluated by two cardiologists according to clinical routine.The MI size estimated by QRS scoring correlated with MI size assessed by CMR (r=0.55, p=0.006). The sensitivity for lateral MI detection was 78% for QRS scoring and 39% for clinical routine ECG evaluation, respectively.Selvester QRS scoring can be used to estimate size of isolated lateral MI and has a higher sensitivity for infarct detection compared to clinical routine evaluation of ECGs in these patients.