Systems and devices are provided for heating an infusible liquid. The inline heater includes a fluid flow channel defined by a conduit for flowing an infusible liquid through a first portion of the conduit having a first cross-sectional dimension to a second portion of the conduit having a smaller second cross-sectional dimension. A nozzle is disposed in the first portion of the conduit. A heating element in thermal communication with an outer surface of the second portion of the conduit conducts heat through the conduit into the infusible liquid. The nozzle is positioned to spray the infusible liquid about a circumference of an inner wall of the second portion of the conduit to provide increased heat transfer from the heating element to the infusible liquid. The inline heater may be formed as a cassette for use in a dialysis machine.