Abstract Background Electrocardiogram (ECG) interpretation is of great importance for patient management. However, medical students frequently lack proficiency in ECG interpretation and rate their ECG training as inadequate. Our aim was to examine the effect of a standalone web-based ECG tutorial and to assess the retention of skills using multiple follow-up intervals. Methods 203 medical students were included in the study. All participants completed a pre-test, an ECG tutorial, and a post-test. The participants were also randomised to complete a retention-test after short (2–4 weeks), medium (10–12 weeks), or long (18–20 weeks) follow-up. Intragroup comparisons of test scores were done using paired-samples t -test. Intergroup comparisons of test scores were performed using independent-samples t -test and ANOVA, whereas demographic data were compared using ANOVA and Chi-squared test. Results The overall mean test score improved significantly from 52.7 (SD 16.8) in the pre-test to 68.4 (SD 12.3) in the post-test (p