Abstract-Optical techniques have revolutionized the investigation of cardiac cellular physiology and advanced our understanding of basic mechanisms of electrical activity, calcium homeostasis, and metabolism. Although optical methods are widely accepted and have been at the forefront of scientific discoveries, they have been primarily applied at cellular and subcellular levels and considerably less to whole heart organ physiology. Numerous technical difficulties had to be overcome to dynamically map physiological processes in intact hearts by optical methods. Problems of contraction artifacts, cellular heterogeneities, spatial and temporal resolution, limitations of surface images, depth-offield, and need for large fields of view (ranging from 2ϫ2 mm 2 to 3ϫ3 cm 2 ) have all led to the development of new devices and optical probes to monitor physiological parameters in intact hearts. This review aims to provide a critical overview of current approaches, their contributions to the field of cardiac electrophysiology, and future directions of various optical imaging modalities as applied to cardiac physiology at organ and tissue levels. Key Words: optical mapping Ⅲ fluorescent probes Ⅲ electrophysiology Ⅲ arrhythmia Ⅲ defibrillation M ammalian physiology has an ingrained hierarchy with molecular and cellular physiology at its base, followed by the interactions of large populations of cells and organ systems, and finally the integration of multiple organ functions of an entire animal. For the past 4 decades, cardiovascular physiology has been dominated by a "reductionist" approach, focusing on cellular mechanisms. Major strides have been accomplished in our understanding of cellular mechanisms, including metabolism, intracellular signaling, trafficking, ion channel structure, function, and expression. With a greater understanding of cellular mechanisms came the growing realization that organs such as the heart are composed of several types of interacting cells with significant and important heterogeneities of properties, cell-to-cell coupling, and function within each group. Thus, an understanding of molecular and cellular mechanisms must still be integrated to explain the more complex organ system while taking into account spatial and temporal heterogeneities of cell functions throughout the organ.Unfortunately, experimental methodologies available for studies at the organ level are not as abundant as at the cellular scale. Nonoptical imaging modalities, including positron emission tomography, magnetic resonance, and ultrasound imaging have only started to bridge molecular and organ physiology using novel contrast agents. 1 On the other hand, optical modes of imaging, in combination with parametersensitive probes have already demonstrated their ability to overcome the problem of spatiotemporal resolution in two dimensions for a wide range of applications from single molecular events to in vivo whole animal physiology.Fluorescence has been used to measure a wide range of physiological parameters in cells and tissues...

The rigidity and relatively primitive modes of operation of catheters equipped with sensing or actuation elements impede their conformal contact with soft-tissue surfaces, limit the scope of their uses, lengthen surgical times and increase the need for advanced surgical skills. Here, we report materials, device designs and fabrication approaches for integrating advanced electronic functionality with catheters for minimally invasive forms of cardiac surgery. By using multiphysics modelling, plastic heart models and Langendorff animal and human hearts, we show that soft electronic arrays in multilayer configurations on endocardial balloon catheters can establish conformal contact with curved tissue surfaces, support high-density spatiotemporal mapping of temperature, pressure and electrophysiological parameters and allow for programmable electrical stimulation, radiofrequency ablation and irreversible electroporation. Integrating multimodal and multiplexing capabilities into minimally invasive surgical instruments may improve surgical performance and patient outcomes.Minimally invasive surgeries involve the insertion of advanced diagnostic and therapeutic tools through small percutaneous incisions for treatment of cardiovascular diseases, cancers and other health conditions, with fast recovery times and low risks compared with those of conventional procedures 1,2 . Catheters represent one of the most compelling devices for such purposes due to their capabilities in deploying medical devices (for example, intravascular stents or heart-valve prostheses), capturing information during surgical procedures (for example, force, temperature or electrograms) and/or delivering forces, electromagnetic energy, thermal stimuli and/or biomaterials (for example, drugs, cells or nanoparticles) to targeted sites on or within soft tissues 3,4 . Although these catheter-based approaches have widespread uses in modern medicine, they suffer from (1) mechanical rigidity or insufficient compliance, leading to non-ideal interfaces with soft tissues and low coupling efficiency 5 , Han et al.

Background-There is an effort to build an anatomically and biophysically detailed virtual heart, and, although there are models for the atria and ventricles, there is no model for the sinoatrial node (SAN