Dominant frequencies of QRS complex
The QRS complex is a "spike" that lasts about 100 ms. There is also the P wave that comes before Q which indicates atrial contraction, and the ST segment after. The QRS complex is associated with the ventricles contracting. Blood is being pushed into the major arteries. This part of the cycle is called systole. QRS is like a spark plug if you would permit a simplistic analogy. It represents timing not blood flow. The waveform that represents blood flow is the instantaneous pressures in each  artery and vein and those waveforms are much smoother. The pulse on your wrist is a pressure waveform.

See here for a good tutorial.

While an average heart rate is about one a second, there is a lot of beat to beat variability even when an individual is resting. It's not really periodic in the Fourier decomposition sense.   Signals that are not periodic have a continuous frequency spectrum and the majority of the energy for QRS is in the 40 to 100 Hz band. Blood pressure waveforms have most of their energy at the lower frequencies.