A guide wire configured for intravascular insertion, the guide wire comprising: a core wire comprising, in a direction from a distal end of the core wire to a proximal end of the core wire : a first rounded portion that is located at a distal-most end of the core wire , a second portion configured to allow the core wire to preferentially bend in at least one plane that passes through a longitudinal axis of the core wire ; and a third rounded portion ; wherein: wherein the second portion comprises a first flattened portion (208B ), a second flattened portion (208B ), a third flattened portion (208B ), and a fourth flattened portion (208B ), wherein: - the first flattened portion (208B ) and the second flattened portion (208B ) are round to flat transition portions disposed between the rounded first portion and the third flattened portion 208B , - the third flattened portion (208B ) has a substantially constant rectangular or square cross-section, - the fourth flattened portion (208B ) is a flat to round transition portion disposed between the third flattened portion (208B ) and the rounded third portion , and wherein from the first portion to the third flattened portion (208B ), the cross-sectional area of the core wire decreases and the core wire becomes progressively more flat, and from the third flattened portion (208B ) to the third rounded portion , the cross-sectional area of the core wire increases and the core wire becomes progressively more round. a core wire comprising, in a direction from a distal end of the core wire to a proximal end of the core wire : a first rounded portion that is located at a distal-most end of the core wire , a second portion configured to allow the core wire to preferentially bend in at least one plane that passes through a longitudinal axis of the core wire ; and a third rounded portion ; wherein: a first rounded portion that is located at a distal-most end of the core wire , a second portion configured to allow the core wire to preferentially bend in at least one plane that passes through a longitudinal axis of the core wire ; and a third rounded portion ; wherein: wherein the second portion comprises a first flattened portion (208B ), a second flattened portion (208B ), a third flattened portion (208B ), and a fourth flattened portion (208B ), wherein: - the first flattened portion (208B ) and the second flattened portion (208B ) are round to flat transition portions disposed between the rounded first portion and the third flattened portion 208B , - the third flattened portion (208B ) has a substantially constant rectangular or square cross-section, - the fourth flattened portion (208B ) is a flat to round transition portion disposed between the third flattened portion (208B ) and the rounded third portion , and wherein - the first flattened portion (208B ) and the second flattened portion (208B ) are round to flat transition portions disposed between the rounded first portion and the third flattened portion 208B , - the third flattened portion (208B ) has a substantially constant rectangular or square cross-section, - the fourth flattened portion (208B ) is a flat to round transition portion disposed between the third flattened portion (208B ) and the rounded third portion , and wherein <EOS>