How do isothermal lines differ from isentropic lines on a P-H diagram?

Isothermal lines on a P-H diagram represent constant temperature, whereas isentropic lines represent constant entropy. Isothermal lines are horizontal and indicate no change in temperature, whereas isentropic lines are curved and indicate a reversible adiabatic process. Understanding the difference between these lines is essential for analyzing refrigeration cycles, as isentropic processes are idealized and isothermal processes are more realistic.