BackgroundMedical students are expected to be competent in interpreting electrocardiograms (ECGs) by the time they graduate, but many are unable to master this skill. Studies suggest that e-modules are an effective way to teach ECG interpretation, however they are typically evaluated for use during clinical clerkships. We sought to determine if an e-module could replace a didactic lecture to teach ECG interpretation during a preclinical cardiology course.MethodsWe developed an asynchronous, interactive e-module that consisted of narrated videos, pop-up questions and quizzes with feedback. Participants were first year medical students who were either taught ECG interpretation during a 2-hour didactic lecture (control group) or were given unlimited access to the e-module (e-module group). First-year internal medicine residents (PGY1 group) were included to benchmark where ECG interpretation skills should be at graduation. At three time-points (pre-course, post-course, and 1-year follow-up), participants were evaluated for ECG knowledge and confidence. A mixed-ANOVA was used to compare groups over time. Students were also asked to describe what additional resources they used to learn ECG interpretation throughout the study.ResultsData was available for 73 (54%) students in the control group, 112 (81%) in the e-module group and 47 (71%) in the PGY1 group. Pre-course scores did not differ between the control and e-module groups (39% vs. 38%, respectively). However, the e-module group performed significantly better than the control group on the post-course test (78% vs. 66%). In a subsample with 1-year follow-up data, the e-module group’s performance decreased, and the control group remained the same. The PGY1 groups’ knowledge scores were stable over time. Confidence in both medical student groups increased by the end of the course, however only pre-course knowledge and confidence were significantly correlated. Most students relied on textbooks and course materials for learning ECG, however online resources were also utilized.ConclusionsAn asynchronous, interactive e-module was more effective than a didactic lecture for teaching ECG interpretation, however continued practice is needed regardless of how students learn to interpret ECGs. Various ECG resources are available to students to support their self-regulated learning.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12909-023-04338-6.