What causes my teeth to be sensitive to heat?

Exam needed. It could be from dental caries (tooth decay), broken or defective fillings, nerve inflammation, dental erosions, abrasions or abfractions, gum recession, or perhaps just very sensitive teeth. See your dentist who can give you a thorough dental exam and determine the cause(s).
Only heat? Sensitivity to heat is sometimes an indication that a nerve is dead or dying. Being sensitive to hot and cold is very common and can be due to gum recession/exposed root structure, overly aggressive brushing, decay, leaking restorations. But since you said heat only, does it linger for a period of time? In any case, have your dentist check the area to see that there isn't a problem brewing.

Related Questions

What could be causing my teeth to be increasingly sensitive to heat and cold?

Tooth sensitivity. Tooth sensitivity can be caused by many things: over zealously brushing (be sure to use a soft toothbrush!), tooth whitening products, or cavities. Use a desensitizing toothbrush like sensodyne to put the sensitivity at bay. Read more...
Dying nerve. While there can be many causes, the most likely is a dying tooth nerve. Read more...

I have a tooth that is sensitive to heat and cold and it also seems to hurt when I bite a certain way. What could cause this?

Nerve involvement. The nerve of the tooth is usually affected when you have heat and bite sensitivity. Only an xray can determine if this is the case. Please seek dental attention as soon as possible. If you have either a cavity or a fractured tooth affecting the nerve, a root canal treatment or extraction may be necessary to resolve your pain. Read more...
Tooth infection. Hot and cold sensitivity are classic signs of tooth neve infection. The solution is root canal or tooth extraction. Get to your dentist asap to prevent a worsening of infection. Hope that helps, dr. Jonathan neman. Read more...