As noted by a former Chairman, the term “one country-two systems” was initially coined to describe a new experimental paradigm for normalized relations between Hong Kong and China, two territories that had long been united, but had evolved along separate paths during the Twentieth Century. Over the past 50 years, studies of the cardiovascular system have also evolved along distinct pathways, largely based upon the territorial boundaries of modern developmental biology and clinical physiology. The developmental viewpoint has been underpinned by genetics, and a reductionist approach toward mechanism, with molecular biology as its primary tool, and the smallest biological unit being individual cell types. The clinical cardiology viewpoint has been based on physiology, and an integrative approach toward mechanism, with interventional/device/imaging technologies as the primary tools, and the smallest biological unit being the intact organ. In short, studies of the cardiovascular system have traditionally been approached by citizens of “two” very different scientific cultures and “countries,” each with their own societies, uniforms, icons, and customs. If the recent 67 th Quantitative Symposium of Cold Spring Harbor Laboratory on “The Cardiovascular System” is any guide, this era of “one system-two countries” is coming to a close. During this symposium, converging pathways and perspectives of cardiovascular development and physiology were presented, driven by post-genomic tools and technology, a new generation of scientists and physicians trained to work at the interface of developmental biology, genetics, physiology, and human disease, and an integrative approach to biology. This review highlights some of the central themes presented by delegates of both “countries” that provided new insights into developmental principles of human cardiovascular physiology and disease.