In general, “conduction delay” refers to a slight widening of the QRS complex, especially in the right precordial leads (leads V1, V2, and V3); it is sometimes also called incomplete right bundle branch block.  The most common cause of this is just being a normal variant, in other words, there is nothing wrong with the heart.  There are, however, some patients who have enlargement of the right heart as a cause for this, such as having an atrial septal defect resulting in enlargement of the right ventricle or perhaps partial anomalous pulmonary venous drainage of some of the pulmonary veins return to the right side instead of the left side.  Sometimes medications can cause conduction delay because of indirect effects on the heart and generally that is considered safe.  Finally, there are some individuals where conduction delay may represent conduction system disease, but this is very uncommon.