I've now got an iPhone 4 and tested my app iStethoscope Pro with the new device. The good news is that it works fine and the microphone may be more sensitive, so it may be even easier to hear your heartbeat with the new device. The bad news is that the frequency response of the iPhone 4 microphone appears to be slightly different to that of the iPhone 3G, so there is less detail at the very low frequencies and more noise at higher frequencies. Do please note that the location of the microphone is different in the iPhone 4 - it is on the bottom left, not on the bottom right!

Because the iPhone 4 has a different microphone and casing, it is necessary to modify the audio filter settings in order to hear the clearest heart sounds. My suggestion is:

Use Heartbeat pure mode and in the Audio Settings change to

Alpha value (default 150) = 125

Amplification (default 0.25) = 1

In General, scroll down and change Spectrogram scaling to

Heartbeat pure (default 0.5) = 0.3

As usual you can find the detailed help pages here and here. If you have your own suggestions for settings for the iPhone 4, leave a comment here. Otherwise if you have any problems, please leave your comments on the main support page as usual.