Background Blood outgrowth endothelial cells ( BOEC s) mediate therapeutic neovascularization in experimental models, but outgrowth characteristics and functionality of BOEC s from patients with ischemic cardiomyopathy ( ICMP ) are unknown. We compared outgrowth efficiency and in vitro and in vivo functionality of BOEC s derived from ICMP with BOEC s from age‐matched ( ACON ) and healthy young ( CON ) controls. Methods and Results We isolated 3.6±0.6 BOEC colonies/100×10 ⁶ mononuclear cells ( MNC s) from 60‐mL blood samples of ICMP patients (n=45; age: 66±1 years; LVEF : 31±2%) versus 3.5±0.9 colonies/100×10 ⁶ MNC s in ACON (n=32; age: 60±1 years) and 2.6±0.4 colonies/100×10 ⁶ MNC s in CON (n=55; age: 34±1 years), P =0.29. Endothelial lineage ( VEGFR 2 ⁺ / CD 31 ⁺ / CD 146 ⁺ ) and progenitor ( CD 34 ⁺ / CD 133 ⁻ ) marker expression was comparable in ICMP and CON . Growth kinetics were similar between groups ( P =0.38) and not affected by left ventricular systolic dysfunction, maladaptive remodeling, or presence of cardiovascular risk factors in ICMP patients. In vitro neovascularization potential, assessed by network remodeling on Matrigel and three‐dimensional spheroid sprouting, did not differ in ICMP from (A) CON . Secretome analysis showed a marked proangiogenic profile, with highest release of angiopoietin‐2 (1.4±0.3×10 ⁵ pg/10 ⁶ ICMP ‐ BOEC s) and placental growth factor (5.8±1.5×10 ³ pg/10 ⁶ ICMP BOEC s), independent of age or ischemic disease. Senescence‐associated β‐galactosidase staining showed comparable senescence in BOEC s from ICMP (5.8±2.1%; n=17), ACON (3.9±1.1%; n=7), and CON (9.0±2.8%; n=13), P =0.19. High‐resolution microcomputed tomography analysis in the ischemic hindlimb of nude mice confirmed increased arteriogenesis in the thigh region after intramuscular injections of BOEC s from ICMP ( P =0.025; n=8) and CON ( P =0.048; n=5) over vehicle control (n=8), both to a similar extent ( P= 0.831). Conclusions BOEC s can be successfully culture‐expanded from patients with ICMP . In contrast to impaired functionality of ICMP ‐derived bone marrow MNC s, BOEC s retain a robust proangiogenic profile, both in vitro and in vivo, with therapeutic potential for targeting ischemic disease.