BACKGROUNDPeople living with cardiac and respiratory disease require improved post-hospital support that is readily available and efficient.OBJECTIVESTo 1) test the effectiveness of an automated, semi-personalised text message support program on clinical and lifestyle outcomes amongst people attending cardiac and pulmonary rehabilitation. Also, 2) to evaluate the program's acceptability and utility using patient-reported outcome and experience measures.METHODSMulticentre randomised controlled trial (3:1, intervention:control) amongst cardiac and pulmonary rehabilitation attendees. Control received usual care (no message program). Intervention also received a 6-month text message lifestyle and support program. Primary outcome was 6-minute walk distance (6MWD). Secondary outcomes included clinical measures, lifestyle, patient-reported outcome and experience measures, medication adherence and rehabilitation attendance.RESULTSA total of 316 participants were recruited. They had a mean age of 66.7 (SD 10.1) years. Sixty percent were male (190/316) and 156 were cardiac rehabilitation participants. The cohort's mean baseline 6MWD was higher in the intervention than the control group. At 6 months, 6MWD improved in both groups; it was significantly greater amongst intervention than control participants (unadjusted mean difference of 43.4 m, 95 % CI 4.3 to 82.4; P = 0.0296). After adjustment for baseline values, there was no significant difference between intervention and control groups for 6MWD (adjusted mean difference 2.2 m, -21.2 to 25.6; P = 0·85), medication adherence, or cardiovascular risk factors. At 6-month follow-up, intervention participants reported significantly lower depression scores (adjusted mean difference -1.3, 95 % CI -2.2 to -0.3; P = 0.0124) and CAT scores (adjusted mean difference -3.9, 95 % CI -6.6 to -1.3; P = 0.0038), and significantly lower anxiety (adjusted mean difference -1.1, 95 %CI -2.1 to 0; P = 0.0456). Most participants (86 %) read most of their messages and strongly/agreed that the intervention was easy to understand (99 %) and useful (86 %).CONCLUSIONSAn educational and supportive text message program for cardiac and pulmonary rehabilitation attendees improved anxiety and depression plus program attendance. The program was acceptable to, and useful for, participants and would be suitable for implementation alongside rehabilitation programs.TRIAL REGISTRATION NUMBERACTRN12616001167459.