Jinkyung Park^1,2,*, Suji Choi^1,3,*, Ajit H. Janardhan⁴, Se-Yeon Lee^5,6, Samarth Raut⁷, Joao Soares⁷, Kwangsoo Shin^1,3, Shixuan Yang⁸, Chungkeun Lee⁹, Ki-Woon Kang¹⁰, Hye Rim Cho^1,11, Seok Joo Kim^1,3, Pilseon Seo^1,3, Wonji Hyun^1,3, Sungmook Jung^1,3, Hye-Jeong Lee¹², Nohyun Lee¹³, Seung Hong Choi^1,11, Michael Sacks⁷, Nanshu Lu^8,14, Mark E. Josephson¹⁵, Taeghwan Hyeon^1,2,3,†, Dae-Hyeong Kim^1,3,† and Hye Jin Hwang^5,15,†,‡

¹Center for Nanoparticle Research, Institute for Basic Science, Seoul 08826, Republic of Korea.
²Graduate School of Convergence Science and Technology, Seoul National University, Suwon, Gyeonggi-do 16229, Republic of Korea.
³School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Seoul 08826, Republic of Korea.
⁴Division of Cardiac Electrophysiology, Health First Medical Group, Cocoa Beach, FL 32931, USA.
⁵Yonsei Cardiovascular Research Center and Cardiovascular Research Institute, Severance Hospital, Yonsei University Health System, Seoul 03722, Republic of Korea.
⁶Institute for Biomedical Convergence, College of Medicine, Catholic Kwandong University, Gangneung-si, Gangwon-do 25601, Republic of Korea.
⁷Center for Cardiovascular Simulation, Institute for Computational Engineering and Sciences, University of Texas at Austin, Austin, TX 78712, USA.
⁸Center for Mechanics of Solids, Structures and Materials, Department of Aerospace Engineering and Engineering Mechanics, Texas Materials Institute, University of Texas at Austin, Austin, TX 78712, USA.
⁹School of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea.
¹⁰Division of Cardiology, Eulji University Hospital, Eulji University College of Medicine, Daejeon 35233, Republic of Korea.
¹¹Department of Radiology, Seoul National University College of Medicine, Seoul 03080, Republic of Korea.
¹²Department of Radiology, Research Institute of Radiological Science, Severance Hospital, Yonsei University Health System, Seoul 03722, Republic of Korea.
¹³School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea.
¹⁴State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China.
¹⁵Harvard-Thorndike Electrophysiology Institute, Cardiovascular Division, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.

^†Corresponding author : Hye Jin Hwang; Dae-Hyeong Kim; Taeghwan Hyeon

^* These authors contributed equally to this work.

^‡ Present address: Cardiovascular Division, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.

Abstract
Heart failure remains a major public health concern with a 5-year mortality rate higher than that of most cancers. Myocardial disease in heart failure is frequently accompanied by impairment of the specialized electrical conduction system and myocardium. We introduce an epicardial mesh made of electrically conductive and mechanically elastic material, to resemble the innate cardiac tissue and confer cardiac conduction system function, to enable electromechanical cardioplasty. Our epicardium-like substrate mechanically integrated with the heart and acted as a structural element of cardiac chambers. The epicardial device was designed with elastic properties nearly identical to the epicardial tissue itself and was able to detect electrical signals reliably on the moving rat heart without impeding diastolic function 8 weeks after induced myocardial infarction. Synchronized electrical stimulation over the ventricles by the epicardial mesh with the high conductivity of 11,210 S/cm shortened total ventricular activation time, reduced inherent wall stress, and improved several measures of systolic function including increases of 51% in fractional shortening, ~90% in radial strain, and 42% in contractility. The epicardial mesh was also capable of delivering an electrical shock to terminate a ventricular tachyarrhythmia in rodents. Electromechanical cardioplasty using an epicardial mesh is a new pathway toward reconstruction of the cardiac tissue and its specialized functions.