Stanford has expanded its ResearchKit-based heart health trial, run from the MyHeart Counts iPhone app, to Hong Kong and the United Kingdom. MyHeart Counts was one of the first five apps to launch when Apple announced ResearchKit, an open source platform helps researchers build medical apps and more easily recruit patients for clinical trials.

“The idea is to move into one country at a time until we go global,” MyHeart Counts co-investigator and Stanford professor Euan Ashley said in a statement. "We hope to add more countries every few months.”

The app measures activity through the Apple Watch, which offers heart rate tracking through sensors in the iPhone or a third-party wearable activity device linked to Apple's Health app. It will also ask users, who are able, to complete a six-minute walk test once every three months as well as monitor their activity for a week. If users sync their cholesterol results and blood pressure, the MyHeart Counts app will also calculate their risk for future heart attack or stroke and provide them with a “heart age.”

Researchers have also released a second version of the app which will provide participants with more feedback about their individual behaviors and risk, including physical activity, diet, blood pressure and cholesterol levels, based on the American Heart Association’s “Life’s Simple 7” recommendations. The new version will also show users how their six-minute walk test compared  to other users' tests.

Stanford explains that on top of providing reminders about recording activity and sleep and completing surveys on physical activity readiness, the university “may also ask you to test different approaches to help you be more active so we can understand how mobile apps in the future can help prevent heart disease.”

The day after MyHeart Counts first launched in March, it received 11,000 sign ups. Now, the app has 41,000 users. Researchers on the trial said this study has helped them collect the most data ever on the six-minute walk fitness test for a single study.

“We are ready to take the study as far as it will go. We would like to build a new Framingham heart study for the ages,” Ashley said in a statement, referring to the long-term cardiovascular study that has followed three generations of participants in Framingham, Massachusetts. “We would like millions of participants.”