A cluster comprising cardiomyocyte-like cells, wherein the cluster has i) contracting cells, ii) cells that are electrically connected, and expresses iii) cardiac markers including Nkx.2.5, troponin and myosin, iv) markers for functional adrenergic receptors, v) markers for functional muscarinic receptors, vi) markers for functional ion-channels including hERG, Na+, Ca2+ and K+ channels, vii) one or more endodermal markers selected from the group consisting of AFP, TF, APOA2, AHSG, SERPINA1, APOA1, APOC3, TTR1 APOB, and RBP4. A method for preparing the clusters and the use of the clusters in drug discovery and toxicity screenings are described.