Since I do not know the nature of your heartmurmur or extent of your dental work, I will provide some general information about antibiotics and dental procedures.
In England, Scotland and Wales, patients with angina, valvular heart disease, a heartmurmur or heart failure do not have to tell the Driver and Vehicle Licensing Agency (DVLA) and can continue to drive a car a month after an episode as long as their doctor says they are fit to.