I did as you suggested and the following website stated that caffeine may be secreted in saliva, semen and breast milk-
Erowid Caffeine Vault - Effects. Maybe this explains the arrthymia after sex - I hope so, as it has never occured with another I don't know what else could be causing it. As we know, irregular heartbeats can be really frightening and as much as we crave the affection and closeness of sex this has really made me scared.