A growing interest in Organic Rankine Cycles (ORCs) and high-temperature heat pumps (HTHPs) is currently verified in literature. However, there is still a shortage of flow boiling experimental studies involving organic refrigerants at high saturation temperatures. In ORCs and HTHPs systems, evaporation can occur at intermediate-to-high reduced pressures for most of the typically employed refrigerants. As the reduced pressure rises, vapor density increases, while the liquid density decreases, converging to the same value when the saturation pressure reaches the critical value. In addition, the enthalpy of vaporization and the surface tension gradually reduce, while the liquid specific heat slightly increases as the reduced pressure rises. These changes in thermophysical properties considerably affect the two-phase flow characteristics, diverging from that commonly verified at low reduced pressures, and leading to a loss of accuracy of the prediction methods currently available in literature, which in general were developed for refrigeration and air conditioning applications. In this context, this paper presents an experimental investigation on flow boiling heat transfer of R1233zd(E) at saturation temperatures between 75°C and 95°C. Heat transfer coefficient data were obtained in a horizontal stainless-steel tube with an internal diameter of 2 mm, for mass velocities and heat fluxes of 187-374 kg/m^²s, and 19-55 kW/m^², respectively. Experimental results indicated the dominance of nucleate boiling effects. The heat transfer coefficient data were also compared with 10 prediction methods from literature, and the lowest deviations were achieved by methods proposed for carbon dioxide.