Lentiviruses have the capacity to enter and integrate their genetic material into cells that are not dividing. This property is retained in vectors based on these agents. They can thus effect gene delivery to cells that are difficult to transduce such as cardiac myocytes in vitro and in vivo. They are also relatively efficient at entering dividing cells and can transduce stem cells and vascular endothelium. They have a substantial gene-carrying capacity of up to around 9 kb. They do not trigger an inflammatory response and are thus useful when proinflammatory agents are undesirable, such as in transplantation. Their ease of cloning and well-understood molecular biology have made them highly suitable for gene delivery to the heart.