Graphics card temperatures typically range from 40°C to 90°C. Performance class graphics cards can reach high temperatures under heavy load. The heatsink and fan assemblies on the graphics cards are designed to pull the heat away from the graphics card. A case which does not have proper airflow can prevent the heat from escaping the graphics card. Adding fans to your case which pulls cool air from the front of your case and drags hot air from the back of your case can help reduce the temperatures of your components inside of your PC.
Also, the fans on graphics cards can collect dust over a period of time inhibiting it's ability to cool the GPU. It's good practice to occasionally check and gently clean your PC components.