This depends if you really are missing a beat. Most feelings of missed beats are in fact caused by what are called 'ectopic' beats: two beats closer together, which means you have the sensation of missing a beat. These are harmless. They can be caused by stress, caffeine, anxiety. What was happening when you had this experience?
True missed beats are rare, and are usually connected to a form of heart block (I should know, I have this). That's why you need a 24 hour Holter recording. If your symptoms are rarer than this, ask for a 7 day loop recorder.
Either way, there is no immediate health threat. If your symptoms continue for more than an hour at a time go to the emergency room: they can give you an ECG and let you know straight away what's happening.
ya 99 percent chance pvcs...just mention it to your doc, and theyll probably get you a holter monitor which is just something you wear that detects and records your heart beat for weeks...pvcs are not one bit dangerous..ive had em for four years, and i have forgotten about them..you will too.
Probably PVCs
http://en.wikipedia.org/wiki/Premature_ventricular_contraction