Why do I get an occasional rapid heart beat when drinking?

Rapid heart rate. Alcohol is known to have vasodilator properties, as a reflex the heart rate can go up transiently. But if you have been drinking for quite sometime, it damages the heart muscle, you will end up in congestive heart failure and that can also increase the heart rate.
Possible arrhythmia. There are many abnormalities of the hearts electrical system that may cause a rapid heart beats. Occasionally alcohol triggers them. Binge drinking can cause atrial fibrillation. We call it holiday heart.