## 1 Introduction  
Since the discovery of the human genome, technological advances have enabled scientists to study the whole genome in detail and its implication in physiology and pathology. In the early 1960s, it was estimated that the human genome consisted of at least two million of protein-coding genes. However, the launching of the Human Genome Project in 1990 dropped this number to 20,500 of coded genes, which is only about 2% of the genome [1]. The other 98% consisted of non-coding genes and was deemed as \"transcriptional noises\" or \"genetic junks\" due to the assumption that they played no necessary cellular functions. Therefore, researchers have ignored these non-coding regions, but non-coding RNAs (ncRNAs) transcribed from these regions are recently emerging as important regulators of cellular processes with many implications in human diseases [2].  
Unlike messenger RNAs (mRNAs), ncRNAs do not translate to generate proteins. Non-coding DNA sequences are actively transcribed into ncRNA sequences, which include microRNA (miRNAs or miR), short interfering RNAs (siRNAs), and long non-coding RNAs (lncRNAs) [3]. MiRs are short ncRNA sequences with a length of 20-22 base pairs and have important regulatory functions in health and disease. In mammalian species, miR post-transcriptionally regulate gene expression by inhibiting protein synthesis or promoting mRNA degradation through the binding to specific complementary mRNA sequences mainly in the 3'-untranslated region (3'-UTR) [4]. SiRNAs comprise of 20-25 base pairs in length and regulate gene expression, mostly through the RNA interference (RNAi) pathway [5]. According ncRNA classification, lncRNAs are more than 200 base pairs in length. They are transcribed by RNA polymerase II, polyadenylated, and subjected to splicing. LncRNAs also have promoter structures and are pervasively expressed across the genome [6].  
Recently, lncRNAs have emerged as important players in regulating gene expression. For example, they can regulate neighboring genes in cis-formation. They can also function in trans-acting formation to regulate the expression of genes, which are not located closely with lncRNAs. LncRNAs play important roles in the initiation and development of diseases, particularly cardiovascular diseases [7]. They can control the expression of disease-related genes by functioning as molecular scaffolds to regulate chromatin modifications and influencing the epigenetic programs of the transcriptome [8]. Moreover, lncRNAs are actively involved in biological processes including cardioprotection and they can act as endogenous miR sponges by interacting with miR to control gene expression [9,10]. For instance, it is shown that lncRNAs, such as Braveheart (Bvht), elicit gene activation or suppression to stimulate stem cell differentiation during cardiac development [9]. Another lncRNA cardiac hypertrophy-related factor (Chrf) was shown to sequester miR-489 to inhibit its action of targeting _myeloid differentiation primary response gene 88_ (_Myd88_), which induces cardiac hypertrophy through the NF-kB system [10].  
In the following sections, we describe classes of lncRNAs, genetic functions of lncRNAs and their roles in cardiovascular development and diseases, followed by a summary of recent findings that utilize lncRNAs as diagnostic markers of heart disease.