Rampengan, S. H., J. Prihartono, M. Siagian, and S. Immanuel. “The Effect of Enhanced External Counterpulsation Therapy and Improvement of Functional Capacity in Chronic Heart Failure Patients: A Randomized Clinical Trial”. Acta Medica Indonesiana, vol. 47, no. 4, Dec. 2015, https://www.actamedindones.org/index.php/ijim/article/view/18.