Open your App Store or Google play store and search for "Kardia", and tap to download it for free.
You can use this link to go the Kardia app directly:
Kardia on the Apple App Store
Kardia on the Google Play Store
If having trouble downloading Kardia on an iPad check this article.
If you need help downloading the Kardia watch app to your Apple watch, check this article.
Kardia is integrated with Apple Health and Google Fit. To learn more about this feature, please refer to the user manual.