Define "excessive heat." If the phone gets hot to the point where it exceeds the safe operating temperature for the phone it will shut off. If it doesn't shut off it is not "excessive heat."
If you are using the camera the area near the camera will get quite hot if the camera is open for more than a few minutes. This is because the camera sensors (there are two of them) take a lot of energy. They do on every phone with a camera, BTW.
The phone will also get hot when using cellular data or voice if the cellular signal is weak (1 or 2 bars). That's because the phone increases its output power as much as 10 times to maintain a connection.
The phone will get hot when playing games with interactive graphics, because the display uses energy every time it changes state.
The phone will get hot when you have the brightness up high, because the backlight is using more energy.
And, of course, the heat from these is additive. 2 or more of them will create more heat than any one alone.