The “Heart of the City” theme is proposed by the MARS group as title of the 8th Congrès Internationaux d’Architecture Moderne (CIAM), held in Hoddesdon, England, from the 7th to the 14th of July 1951. Two opposite urban conditions are considered by Sert, President of CIAM, as main issues which the Heart discourse should face: from the disappearance of city centres because of the destruction of the War to the negation of the urban centrality because of urban sprawl and the infinite constant enlargement of city boundaries. But the Heart itself also represents two different figures of speeches, the symbol and the metaphor: from one side it becomes a humanist symbol “which springs directly to the senses without explanation”, in opposition to the “mechanized killing” , to the “tyranny of mechanical tools” as stressed by Giedion during CIAM 8, similarly to the almost contemporaneous Congress of Darmstadt where Heidegger makes his famous speech “Building, Dwelling, Thinking”; from the other side the Heart still keeps its metaphorical organic meaning translated into a presumed right physical form and dimension of the city. These oppositions - from annulled bombed centers to infinite urban structures, from metaphor to symbol, “from function to passion” – are the main causes of the complexity and of the stratification of several different layers of significances of the Heart of the City, since CIAM 8 until the present. If CIAM8`s theoretical roots are already traceable within previous debates and architectural experiences, then the thesis stresses the continuity and the complexity of the Heart of the City, since 1951 until the 1970s, as well as its influence in the physical and theoretical transformation of the City in the USA and in Europe. The thesis is therefore both a historical and theoretical study of the Heart theme, through the analysis of both projects and theories related to CIAM 8. Moreover attention has been paid by both master architects` proposals and young students` architects` projects. This is very important since the crucial role of the young generations and of education is vehemently stressed during CIAM 8 itself. As far as the complexity of the Heart theme is concerned, we might consider the different layers of significance, or arteries of the Heart if we want to keep alive the metaphor, as branches of a “cultural phylogeny tree”, which can melt together and which come from the same trunk: CIAM 8 . Since it is not possible to describe each singular branch of a tree, also of a natural tree, then three main ‘actors’ have been individualized in order to dissect horizontally the symbolical branches, similarly to the sections of a complex project or territory. These sections intersect the most important ideas and issues regarding the Heart of the City. Furthermore, these actors have been chosen also because they are characterized by both theoretical and project activity. The first ‘actor’ is Victor Gruen and the First Urban Design Conference held at Harvard in 1956, whose “precursor” is considered CIAM 8 itself. While Team 10 dissolves “old professors” CIAM, and the Core`s concept is beginning to be questioned by Team 10 criticizing the basis of CIAM itself, as Eric Mumford reminds us, overseas the continuity of the CIAM discussion is assured inside the prestigious American University. The main issues that remain, as Sert explains, are the recentralization of the cities for the preservation of civic values and the three-dimensional design as basis for Urban Design. Among the participants there is also the “mall maker” Victor Gruen who publishes “The Heart of Our Cities: The Urban Crisis: Diagnosis and treatment” (1964), a decade after the release of proceedings of the 8th CIAM “The Heart of the City: Towards the Humanization of Urban Life.” (1952). Gruen invents a new commercial type whose architectural devices would be adopted for the design of urban proposals such as in Fort Worth and Louvain la Neuve. Some of these devices are similar to those used by CIAM members in order to raise the humanist values, as stressed during CIAM 8, within their urban master plans. However, for Gruen the centralization of the city is no longer aimed only at the survival of civic values, similarly to Sert, but it is also focused on environmental protection. Indeed, in the early `70s, the Athens Charter and the Heart of the City will become for Gruen the starting points for an updated manifesto centered on environmental planning: the Charter of Vienna. Finally, the case study of Montreal is discussed. Its planner Vincent Ponte, in the late `60s, transforms the right of the pedestrian, ‘la royauté du piéton’ (Le Corbusier) as vehemently stressed by CIAM members in Hoddesdon, into the first germ of social segregation inside the “analogous city”. If CIAM 8 (and later also the UD Conferences and Gruen too) stresses the necessary separation between pedestrians and vehicles, as a translation of a radical antagonism between the symbols of the Heart and the Machine, then Montreal becomes the first example where this split is adopted on an urban scale, concentrating the main pedestrian flow into a huge underground protected and controlled shopping centre. The second ‘actor’ is the CIAM Summer School held in Venice, from 1952 until 1957. This case study, inside Venice as “City of the new modernity”, considers the Core as the arising interest on the relationship between the new project and its surrounding urban context. This theme has been well described since 1950s by Ernesto Nathan Rogers in Casabella-Continuità, and it is related to CIAM 8 too, as asserted by Vittorio Gregotti in 1992: “Moreover at the CIAM in Hoddesdon, also through the ‘Heart of the City’ theme, the question that starts to emerge - and one which will prove central for the next forty years - is that of listening to the context and of the project seen as a dialogue with the context as a deposited form of the history of a specific place.” In parallel, the link between the spirit of the city – Norberg Schultz` genius loci and the Heart of the City, as already stressed by Volker Welter , is analyzed. The main project, which has been discussed, is the Oslo suburb proposal, presented at Hoddesdon by the PAGON Group with Christian Norberg Schultz as a student of Giedion. The third and last actor is Jaap Bakema who, unlike other CIAM members, considers the ‘relationship’ as the main characteristic of the Heart: “There are moments in life when the separation between man and things disappears; at that moment we discover the miracle of the relationship between man and things. And this is the moment of the Heart.” Instead of proposing a central square or a civic center as a main example of the Heart, Bakema exposes the Asplund cemetery in Stockholm: the Dutch architect conceptually shifts the Heart theme from a conception of life to the overlap of life on death, from the inside to the outside, from the urban centrality to the landscape. The main case study is his project for the “human core” of St. Louis in 1960. Almost ten years after CIAM 8, Bakema reconsiders the Heart theme stressing the importance of its historical background, its three-dimension and the relationship between the social and physical urban structure of the City. Finally, if we can consider the first actor as mainly characterized by an overlap between the organic metaphor and the humanist symbol of the Heart, then Bakema`s projects reject any organic functionalist metaphor of the city. The projects are intriguing proposals where the Heart attempts to be the symbolic of harmonious relationships between “You and Me”, between “a centripetal diastolic movement, but, at the same time, a systolic centrifugal one” (Paci, 1954). All three actors represent a particular and precise facet of the heart theme. Indeed the Urban Design Conference and Victor Gruen, represent the invention and the renewal of the city in America through the concept of the Heart; the CIAM Summer school in Venice represents the increasing importance of the tradition, of the Ernesto Nathan Rogers` continuity, of the recognized role of history and context within the modern project; finally Bakema represents the physical interpretation of the philosophical current of the Relationalism (see Enzo Paci), putting the relationships between the urban factors as the main issue for the sociological and physical structure of the city. However, the three actors might be all compared through their grades of relationships. We note indeed that the first is addressed to the centrality of the city, the second to relationship between one building and its surrounding, while the third as a total relationship between different scales of urban structures. Moreover in all three actors, especially in the first and in the last one, there is a similar intention to consider the design of the city with a vertical integration of functions, into a three-dimensional space: in this sense the heart of the city becomes a counterforce of the zoning method of planning, of the four functions` divisions (dwelling, work, recreation, and transport), rather than its mere fifth element as criticized for instance by Team 10. In the contemporary urban discourse and practice, the Heart of the City still remains a reference for contemporary urban projects, such as “The Simple Heart” by Dogma or the proposal for the Grand Paris by Richard Rogers in 2009. However this latter interprets the heart theme mainly as an organic functionalist metaphor, omitting the deep humanist values stressed at CIAM 8. Indeed the heart and the body become merely images for the restoration of connections to external urban severed limbs, in order to reconstruct the governance of the Ile-de-France with balanced districts. Another interesting project is the new centre for Almere in The Netherlands, designed by OMA in the early 1990s, whose aim remains “donner un coeur à ses cinq centres et se rendre attractive.” However, this project is in contradiction with the Generic City described by Rem Koolhaas almost in the same period , where all Heart identities seem to be totally abhorred. The heart of the city becomes in this case a dichotomy between theory and project attitude, before which one of the most radical Manifestos of the last Century finds its limits and incongruity. Moreover, in a contemporary emergence of public space design, of “absent urbanism” (Marshall), of unclear distinction between individual and collective sphere, the Heart (as humanist symbol rather than mere organic metaphor) still seems an important, valid, contemporary abstract idea of the City. It is indeed an eternally present idea, as interpreted already by Giedion , aimed at an ideal overlap between the social and the physical urban structure. It can be interpreted also as a better future condition or idea of the society, towards which we should tend and which should be interpreted in a present tangible form of public space. “This is our task today.” , Giedion affirms at CIAM 8 in 1951, and sixty years later this purpose seems still effective. A similar task has been stressed for instance by Christopher Alexander who, in 2006, publishes the essay “The Heart of the City. The Necessary Binding Force That Creates The Core Of Every City.” Alexander stresses the failure of the First Urban Design Conference in 1956 (first actor), because of its unawareness or incapacity to focus the attention on the public space as the generator of the city. This remains instead “what we 21th - Century architects, now must deliver.” - Alexander claims, underlying the importance of contemporary discourse about the Heart of the City, as generator of “positive space”. In this context, the study of the three actors, between 1950s and 1960s, aims to reveal the complexity of the Heart theme and its influence on urban design until nowadays, “as a reference point for the new forms of public space”. This influence has been already partly unearthed by several authors, historians or designers especially in the last ten years, but without a complete overview. The projects and the theoretical discourses of the three actors represent the attempt to translate the abstract idea of the Heart into a physical urban project. Their failures and successes have become outstanding lessons for present-day Urban Design too. Indeed they allow to specify the context of the Heart theme, delineating some of the theoretical issues and project devices which still concern our contemporary urban planning.