Engineered heart tissues (EHTs) formed around flexible pillars are used to measure the contraction force of myocytes. When based on cardiac cells derived from human induced pluripotent stem cells (hiPSCs), EHTs capture human cardiac physiology and drug responses in vitro. However, variability in contractile function often arises due to variation in tissue positioning on the pillar. Here, novel tapered pillars are introduced to achieve spatial confinement of tissues in EHT devices. The devices are fabricated by moulding polydimethylsiloxane (PDMS) into micromachined tapered cavities of a silicon substrate. The symmetrically-tapered geometry, with the minimum cross-section at the pillar mid-height, restricts tissue movement outside of the indented area. This increases sensitivity and accuracy of tissue contractile readout, providing high reproducibility with reduced variability between data points. Design and stiffness of tapered pillars are investigated to determine the optimal mechanical environment, obtain accurate contractile measurements, and achieve long-term culture of EHTs. Results show that tapered pillars provide superior confinement efficiency (over 90%) compared to straight pillars (30%), with tissue confinement directly correlated to pillar geometry rather than stiffness. The optimized precision in force readouts and long-term tissue studies enables higher sensitivity in the detection of contractile responses to drugs or diseases.