Another formula for MAP is MAP = (SBP + 2DBP)/3. This is because the diastolic phase is about twice as long as the systolic phase when the heart rate is within normal limits. At a faster or slower rate, this is no longer true.
If the heart rate is slower, the diastolic phase time is going to increase. If the heart rate is faster, the diastolic phase time is going to decrease.
SBP = Systolic Blood Pressure
DBP = Diastolic Blood Pressure
PP = Pulse Pressure, the difference between systolic and diastolic
PP = SBP - DBP