The aim of this study is to investigate if imaging guided optimal left ventricular (LV) lead placement improves the response rate to cardiac resynchronization therapy (CRT). Consecutive patients meeting the standard criteria for CRT are included in a prospective, double-blinded, randomized trial to LV lead positioning either 1) guided by cardiac imaging using echocardiography, single-photon emission computed tomography, and visualization of cardiac venous anatomy (cardiac computed tomography (CT), venography) to target an epicardial vein at the site of latest mechanical activation without scar tissue or 2) using standard LV lead placement.

Inclusion Criteria:

• Symptomatic heart failure (New York Heart Association functional class II - IV) despite stabile optimal medical therapy.
• ECG with QRS ≥ 120 milliseconds and left bundle branch block (LBBB) or paced QRS ≥ 180 milliseconds.
• LV systolic dysfunction (Ejection Fraction ≤ 35%).
• written informed consent.

Exclusion Criteria:

• Expected lifetime < 6 months.
• Recent myocardial infarction (< 3 months).
• Pregnant or lactating.
• Inadequate echocardiographic images for determination of site with latest mechanical activation
• No written informed consent.