What evidence does he have that beet juice, with its high amount of sugar and potassium, is going to be a cure for his heart arrhythmia that the medical community hasn't seemed to have cottoned onto..................all this time later?

If he's unhappy with his cardiologist, he needs to explain that, or find another, or try another drug regimen, or submit to a pulmonary vein isolation (my preferred choice because, after two, I have been in NSR for 13 months now, drug-free).

Honestly, the cardiologist, if he/she isn't inept or unprofessionally unresponsive, would probably like a chance to help your dad, even if it is to try something else. But, the expert should have an opportunity to reason with your dad about why what your dad wants to do is unreasonable, or possibly dangerous.

Just my 2-cents-worth.