In response to a question on healthshare.com.au

Smoking can certainly cause heartburn.

Heartburn is generally caused by the acid contents of the stomach flowing back up into the oesophagus. This is usually prevented by muscle fibres at the lower end of the oesophagus (the lower oesophageal sphincter).

Smoking has a number of effects that contribute to heartburn:

• Smoking increases the production of stomach acid, making the fluid that flows back up into the oesophagus more irritating and erosive
  
• Smoking relaxes the lower oesophageal sphincter, increasing the amount of fluid that can reflux up into the oesophagus
  
• Smoking decreases saliva production. Saliva is slightly alkaline, and partly counteracts any acid in the oesophagus.
  
• Smoking can be associated with swallowing air, even despite the lower level of saliva production during smoking. This can increase the pressure inside the stomach and encourage reflux.
  
• Compared to non-smokers, regular smokers have slower clearance of acid from the oesophagus - even when not having a cigarette at the time that acid clearance is measured.
  
• Regular smoking may make it more difficult for the body to heal any damage caused by acid reflux.

All this means that smoking a cigarette contributes to acid in the short term (ie. an occasional cigarette will contribute to heartburn on that day), but also that regular smoking increases the likelihood of heartburn at other times - even if not smoking at that time!