The advent of biventricular devices has added new complexity to the evaluation of pacemaker function and follow-up. Consequently one must acknowledge the various circumstances that can disrupt ventricular resynchronization and provoke haemodynamic deterioration. In this paper we report upon haemodynamic deterioration following resynchronization therapy because of an erroneous connection of an epicardial right ventricular (RV) outflow tract lead to the left ventricular (LV) channel of the device. How ECG and echocardiography can guide the diagnosis and help in prematurely detecting abnormal pacing or loss of LV capture is discussed in detail below.