Implantable cardiac pacemakers have been employed for the treatment of various arrhythmias beginning in the 1950s. Throughout the years, developments in microfabrication technologies, as well as advances in surgical procedures and the understanding of electrophysiology, have brought forth next-generation cardiac pacemakers. These are much smaller, capable of feedback regulation, and endowed with longerlived batteries, which decrease the need for frequent surgery and battery replacement (1). In addition, the advent of antiinflammatory drug-eluting leads has significantly reduced the risk of inflammation and rejection after cardiac pacemaker implantation. However, these devices do not completely eliminate the immune response (2) and still require battery replacements every several years. Furthermore, implantation of foreign bodies on the heart still poses the risk of fouling in the chest cavity, with resultant unwanted electrochemical reactions. In PNAS, Parameswaran et al.(3) describe the development of an approach for cardiac cell and whole-heart pacing. Traditional cardiac pacemakers rely on delivering an electrical pulse to the cardiac tissue to elicit a response in the form of cell contraction. This method is based on the depolarization of the membrane potential of the cardiomyocytes, which leads to intracellular calcium release and activation of the cell contraction machinery. Developments in the field of optogenetics have previously shown that by infecting cardiac cells with light-gated ion channels, it is possible to elicit cardiac cell contraction by light illumination (4). While this method is not invasive, it involves infection of the cardiac tissue with a virus expressing the lightactivated ion channel. Other noninvasive methods based on light illumination have shown that cardiac cells can be paced without the need to apply an electric field. Gentemann et al.(5) described the use of gold nanoparticles irradiated with a 532-nm laser to induce heating of the cardiac cells, which leads to calcium oscillations and cell contraction when placed in a calcium-containing buffer. In a different approach, Savchenko et al.(6) used graphene’s ability to convert light into electricity to pace cardiac cells and tissues in vivo. Other works have described the use of direct laser illumination to induce cardiac contraction in embryonic quail hearts (7) and even adult rabbit hearts (8). While these methods show great promise, they rely on continual laser irradiation to achieve contraction at the same frequency of the applied pulse. Furthermore, the required laser radiant exposure required to achieve stimulation in these methods is very high and may result in a high percentage of cell death. In their work, Parameswaran et al.(3) use photolithography to define a mesh composed of the polymer SU-8 that serves as a substrate for a high-density array of p-type/intrinsic/n-type silicon nanowires (PIN-SiNWs). Such wires were specifically chosen as they have been