Alternative RNA splicing is a fundamental process in gene expression that enhances the coding capacity of the human genome. By selectively including or excluding specific exons, alternative splicing generates multiple RNA sequences from a single gene, leading to different functional outcomes, such as the production of distinct protein isoforms. In the heart, alternative splicing plays a crucial role in creating the cardiac isoforms that determine the mechanical, electrical, and metabolic properties of cardiomyocytes. This thesis investigates the mechanisms governing alternative splicing in the heart and provides a comprehensive understanding of its role in cardiac function. Particularly, we study the RNA-binding protein Quaking (QKI) and we describe how it controls alternative splicing in the heart. Additionally, we explore how QKI regulates back-splicing, a modality of alternative splicing that generates circular RNA molecules (circRNAs). The splicing program of cardiomyocytes is controlled by a network of numerous splicing factors. To gain a broader perspective on this, we compare multiple knock-out mouse models of various splicing factors, aiming to uncover overlaps and interconnections among them. Furthermore, we delve into minor splicing, a largely ignored class of splicing responsible for splicing out rare introns known as minor introns. We investigate how minor splicing regulates the electrophysiological function of cardiomyocytes by controlling the expression of sodium and calcium channels. Lastly, we discuss emerging regulators of RNA splicing, such as long non-coding RNAs. In conclusion, this thesis explores alternative splicing in the heart in greater depth and highlights its significance as a regulatory mechanism of cardiac function.