ISCHEMIA-EXTEND is the long-term follow-up of over 5,300 randomised, surviving participants in the ISCHEMIA and ISCHEMIA-CKD trials across many countries. The original trials were international comparative effectiveness trials to determine the best way to treat and manage chronic coronary disease, with patients with moderate or severe ischemia, and patients with advanced chronic kidney disease and moderate or severe ischemia, respectively. ISCHEMIA-EXTEND assesses whether an initial invasive strategy, cardiac catheterisation and revascularisation when feasible, plus optimal medical therapy, reduces long-term all-cause mortality as compared with an initial conservative strategy. Participants' vital status will be collected for an additional 6 years of follow-up beyond the initial follow-up periods in the original trials.