BenW,

The Buffalo Protocol says to limit physical exertion to a pulse rate that is 10% below your return of symptoms threshold.

Take a FitBit or similar system for tracking your pulse. Record your peak pulse and any symptoms you have afterward. Once you find your 'return of symptoms' pulse rate, moderate your physical effort. Over time, weeks or even months, your 'return of symptoms' pulse should increase as your brain gets used to a higher pulse and blood pressure.