The Signal Processing Toolbox resample funciton is best for signal processing applications. It has an anti-aliasing filter.
I have no idea how you calculated your fft for each signal, however it will be necessary to compute a different frequency vector for the plot for the fft results for the original and resampled signals.
I would not recommend resampling from 62 Hz to 500 Hz. It simply makes no sense. It creates data that are not in the original signal. The Nyquist frequency for your original data will be 31 Hz. That is not enough to see all the necessary features in a normal EKG, and unless you use a Bessel lowpass filter with a cutoff frrequency of 31 Hz at the filter input, much of the information (as well as 50 Hz or 60 Hz mains frequency noise) will be aliased into the recording and impossible to remove by filtering, or see in your signal.
Repeat your study with a sampling frequency of at least 250 Hz and a Bessel anti-aliasing filter with a cutoff of 125 Hz and you will have reliable data. You will not need to resample that signal, and if you use an appropriate reference electrode (usually the right leg electrode) you can avoid environmental noise and mains frequency interference.
