The investigators have developed self-help booklets specifically for adults with PH who are experiencing difficulties with depression. The self-help booklets are based on a type of psychological treatment called Cognitive Behavioural Therapy or CBT for short.

• CBT looks at the way people think and what they do, and how this affects their mood.
• It involves making changes to thoughts and behaviours.
• CBT can help people develop more helpful ways of coping with depression.
• CBT is one of the most effective therapies for depression, this means it works well.

There are four booklets that participants will work though weekly in their own time and at home. The aim of this study is to test whether the self-help booklets are helpful in reducing depression in people with pulmonary hypertension.

Those taking part will be asked to complete a series of questions asking about themselves including whether they are experiencing any difficulties such as depression and anxiety.

They will then be allocated at random to one of two groups. Group one will receive the self-help booklets, called the intervention group. Group two, or the wait list group, will receive the intervention at a later date if it is found to be helpful. Having two groups is very important as it will allow us to see whether benefits associated with taking part in the project was because of the self-help booklets or something else.

Participants in group one will also be contacted partway through the intervention to ask about their experiences of taking part.

Both groups will be asked to complete a series of questionnaires four weeks later and then again in one month. Participants in group one will be contacted again to find out more about their experiences of the project.

Previous research has demonstrated high rates of depression in people with pulmonary hypertension (PH). The psychological interventions that support people with depression are not made specific to people with PH and may not be relevant for them, and there is limited evidence examining psychological treatments for depression in people with PH. The aim of this study is to develop and test a self-help psychological intervention for depression based on cognitive behavioural therapy (CBT), which has been developed specifically for individuals with PH. When participants have agreed to take part, they will be allocated at random into an intervention or wait-list group. The self-help materials will be provided online (for people outside of the UK) or posted in paper form (for those living in the UK) and will take four weeks to complete at home. Both groups will complete questionnaires at the same time points (before starting the study, after four weeks and after eight weeks (pre-, post-intervention and one-month follow up). In addition, the intervention group will be contacted after two weeks of their participation and asked about their experiences of the intervention and participation in the study - measuring acceptability of the intervention. The intervention group will also be asked to complete a feedback questionnaire after completing the intervention to further examine acceptability. Analysis will be conducted by the researcher to examine whether the self-help intervention reduced depression in individuals with PH, compared to those with PH who did not receive the intervention. The potential benefit of the study includes a new intervention for depression in people with PH. When the study is completed, if the intervention is found to be helpful and safe, then the people who took part in the study and did not receive the intervention will be offered the intervention.

Inclusion Criteria:

• Diagnosis of pulmonary hypertension
• Over the age of 18 years
• Able to complete questionnaires without help from others
• Can understand English
• They will read all study documents in detail and ask the researcher any questions they have. Based on this, they could provide informed consent to take part if they are eligible.
• Feels like they have difficulties with depression, low mood or negative thoughts.
• Not currently experiencing thoughts of self-harm or suicide. This means that they have not had thoughts of self-harm or suicide within the last month.

Exclusion criteria:

• Current thoughts of self-harm or suicide.

The study investigators aim to publish the final report in a peer reviewed international journal and also make the anonymised data available in Cardiff University's data repository. The investigators would also like to share the findings in conferences. The data in anonymised format would be available to other researchers upon reasonable request. When the study is complete, electronic files will be stored for a minimum of 15 years by Cardiff University after the end of the project or after publication of any findings based upon the data (whichever is later). The end of project is defined as completion of project closure report or publishing of final articles. This follows Cardiff University's research records retention policy.

When the study is complete, electronic files will be stored for a minimum of 15 years by Cardiff University after the end of the project or after publication of any findings based upon the data (whichever is later). The end of project is defined as completion of project closure report or publishing of final articles. This follows Cardiff University's research records retention policy. Data can be made available following study completion, up until the point of disposal of data after 15 years.

Data will be made available to researchers upon reasonable request.

Both participants and researchers will not be blinded to condition. This is necessary as participants will know before they consent to the study that they may be randomised to a wait list condition or the intervention, and the lead researcher will contact participants during the intervention (at two weeks) to gather acceptability and adherence feedback. Therefore the researcher needs to know who is in the intervention group to contact them.