Background: Indications for revascularisation in chronic total occlusion (CTO) of the coronary artery depend on the interplay between myocardial function, viability, and ischaemia. The technical feasibility of the procedure often relies on the collateral flow to the occluded artery.

Aim: To assess the relation between the degree of collateral flow and characteristics of the myocardium supplied by the oc­cluded artery.

Methods: The study included 54 patients (mean age 62 years, 85% males) with CTO referred for cardiovascular magnetic resonance (CMR) to assess indications for revascularisation. The presence of well-developed collateral flow was defined as a collateral connection grade = 2 and Rentrop score = 3.

Results: The presence of well-developed collaterals (n = 24, 44%) was less likely to be related to systolic dysfunction of the segments supplied by the occluded artery (mean wall motion score index 1.31 ± 0.44 vs. 1.64 ± 0.67, p = 0.04) in comparison to a lack of well-developed collaterals. Patients with well-developed collaterals had a lower frequency of previous myocar­dial infarction of the CTO territory (38% vs. 67%, p = 0.03) with similar frequency of transmural infarctions (21% vs. 23%, p = 0.83). They less frequently presented perfusion deficits of the CTO area during hyperaemia (42% vs. 70%, p = 0.03) and the size of deficits was smaller (median 0.0% [interquartile range 0–12%] vs. 7.5% [0–15%], p = 0.04).

Conclusions: Myocardial segments supplied by CTO with well-developed collaterals are less prone to inducible ischaemia, have better systolic function, and are less likely to undergo myocardial infarction, in comparison to those supplied by CTO with poor collateral circulation. CMR is a non-invasive method that can be used for a comprehensive workup of patients be­ing considered for CTO revascularisation.