Whether cardiac technician wear white coat and use stethoscope after completing the course?
It dependent on the dress code of the hospital or the environment you are working in. In general the answer is you will get a separate dress to wear in the hospital area and yeah! If needed you can use stethoscope.
In general the Cardiac Technicians didn't need the stethoscope as oftenly as a Doctor.
I hope my answer helps. All the very best for your future endeavors!