Educators have placed an emphasis on the development of laboratory materials that supplement the traditional lecture format. The laboratory materials should encourage active learning, small group discussion, and problem-solving skills. To this end, we developed a virtual experiment designed to introduce students to the theory and application of the electrocardiogram (ECG) and the mean electrical axis (MEA). After reviewing background material, the students will analyze ECG recordings from two individuals who underwent a series of experimental procedures. The students are challenged to reduce and analyze the data, calculate and plot the MEA, and answer questions related to the theory and application of the ECG. In conducting the virtual experiment, students are introduced to inquiry-based learning through experimentation. ADV PHYSIOL EDUC 23: 1-17, 2000.