A mobile system for analyzing ECG data includes an analog front end module coupled to a mobile consumer device. The analog front end module is configured to collect ECG data from one or more leads and is operable to convert the analog ECG data to digital ECG data. The mobile consumer device is coupled to receive the digital ECG data, and is configured to perform QRS detection using a filter whose cutoff frequency is adapted to noise level in real time. The ECG signal is amplified non-linearly and three windowed threshold signals (D, E, J) are derived. The cutoff frequency for the QRS detection is dynamically selected as a function of the threshold signals. A sample in the amplified signal is identified to be a heart beat point only when the sample value is equal to the first threshold signal and greater than the filtered threshold signal.