This study investigates the effects of a capacity-building programme on the competency of ECG interpretation among critical care nurses. Electrocardiogram (ECG) interpretation is a fundamental clinical skill essential for the rapid diagnosis of potentially life-threatening conditions. Misinterpretation of ECGs can result in inappropriate clinical decisions, leading to adverse patient outcomes. This study, conducted at a tertiary care hospital with over 1600 beds and six fully equipped intensive care units, aimed to improve the knowledge and practice of ECG interpretation among nurses frequently recording ECGs. A quantitative quasi-experimental study was conducted with 100 nurses selected using non-probability purposive sampling. Pre-test and post-test assessments were used to evaluate knowledge and practice, and data were analyzed using descriptive and inferential statistics. The results showed that the study group had significantly higher post-test knowledge and practice scores compared to the control group, with a strong positive correlation between knowledge and practice scores. The findings highlight the importance of continuous education and training for healthcare professionals.