Heavy metals are usually more of a concern for reef organisms, which are often less tolerant of them.
We just had a heavy metals assay done at our fish farm (since it's a recirculating system) and found some surprising results, but nothing to really worry about.
Not all heavy metals are bad. "Essential" metals such as copper and zinc are probably elevated in your aquarium anyway because they are added to your feed. These levels rarely reach detrimental levels, though.
Your tap water has to be within certain standards, and the water company probably has some numbers they could report to you if you are interested. Is your water very hard? Heavy metals can contribute to water hardness.
Typically I wouldn't worry about heavy metals at all in most freshwater aquariums. Carbon can remove them if the organic load is small enough. If you are concerned though, I second the idea of adding a polyfilter. Even if you don't get a color indication (such as blue for copper), it will still pull out heavy metals in undetectable amounts.
On a side note, I keep a new polyfilter on hand at all times for any contamination I may need to take care of on the spot. My former boss once dropped a full beer into his reef tank. He immediately threw a polyfilter in the sump and had no issues, even without doing a water change! That story convinced me!