Alkali and alkali earth metal carbonates and bicarbonates decomposition
From your question, the heating temperature is unclear. See these links for sodium and lithium carbonates, the hydrocarbonate or barium.

They are all also mentioned on Wikipedia. 

In other words, they all seem to decompose at some point, so what is meant by heating? 

The reaction for sodium carbonate decompositon at melting point should be: 

$$\ce{Na2CO3 -&gt; Na2O + CO2}$$