High heat dissipation from compact modern electronic devices demands smart cooling solutions to ensure proper functionality. Two phase heat transfer has the capability to cope with high heating/cooling demands with better temperature uniformity along the chip. Refrigerant related environmental concerns (ozone depletion, global warming etc.) instigated recent surge for new alternatives. Natural refrigerants are regaining their fame, however reliable experimental studies under wide operating conditions are required for designing novel practical devices. Keeping in view the current demands, this study is focused on the thermal performance of two natural hydrocarbon refrigerants (Isobutane R600a, and Propane R290) in uniformly heated small vertical stainless steel tubes. The heat transfer performance of natural refrigerants is also compared with R134a under similar experimental conditions.  The experiments are carried out under wide operating conditions and continued till completion of dryout. The effects of operating parameters (heat flux, mass flux, vapor quality, saturation temperature etc.) along with assessment of macro and micro-scale correlations are the very subjects of this study.