Updated project metadata. The sinus node is a collection of highly specialized cells that constitute the natural pacemaker activity of our heart. The protein expression landscape of the sinus node differs from the surrounding cardiac tissue, although it is primarily comprised of myocytes and fibroblasts like the rest of the cardiac tissue, endowing it with its unique ability to regulate heart rate. Here we performed quantitative proteomics experiments to profile protein expression in the pacemaker of the heart, and compared it to protein expression in the neighbouring atrial muscle. In summary, the quantitative proteomics data presented here offer a highly detailed insight into the unique composition of the pacemaker of our heart.