In this project the effects of the PLN-R14del mutation on cardiac spheroids and thus on cardiomyocytes have been researched. These spheroids, which are 3D cell structures, have been derived from human-induced pluripotent stem cells, meaning that the cardiac spheroids represent the cardiac workings of the patient they are derived from. These spheroids have been compared to ‘healthy’ spheroids, in which the mutation has been corrected through the use of CRISPR-Cas9. Through the use of Calcium2+ screening we have found that the PLN-R14del mutation mainly causes a longer decay time in the Calcium2+ cycle of the cardiomyocyte, which can result in diastolic disfunction, causing symptoms as shortness of breath, fatigue and weakness.