Phenanthrene (Phe) is a three-ringed polyaromatic hydrocarbon which is formed from incomplete combustion of hydrocarbons and is also a component of crude oil. Previous studies have shown Phe to be cardiotoxic to marine fishes. This study investigated and show significant cardiotoxic effects of Phe across multiple levels of cardiac organization in the brown trout, a sentinel freshwater species. Exposure of whole heart (fish mass 332.4±29.6g; n=10; mean heart mass 0.61±0.05; n=10) with 15 µM Phe showed significant prolongation of ~8.6 % and ~13.2 % for the QT interval (Control – 349±10; Phe – 379±9 ms) and the monophasic action potential (MAP) duration (Control – 386±15; Phe – 437±24 ms) respectively (p < 0.05; 2-way ANOVA) at 0.5 Hz, recorded using Langendorff heart perfusion and contact electrodes. Phe (15 μM) also significantly decreased the force of contraction by approximately 21 % in isolated ventricular muscle strip preparations (Control – 109±8; Phe – 80±9; p < 0.05; 2-way ANOVA) in a force-frequency trial. This suggests that Phe is able to reduce ventricular contracting force by altering cellular calcium cycling. This finding was supported by a significant reduction of ~39 % in the cellular calcium transient following same Phe concentration (15 µM) exposure in isolated ventricular myocytes assessed as mean change in peak fluorescence divided by baseline fluorescence (ΔF/F0) (Control – 0.18 ± 0.02; Phe – 0.11 ± 0.01 p < 0.05; one-way ANOVA). Single cell voltage clamp revealed a Phe-dependent reduction of ~38 % in the L-type Ca2+ current (ICaL) (Control – 6.8 ± 0.4 pA/pF; Phe – 4.2 ± 0.3 pA/pF; p < 0.01; unpaired t-test) which accounts, at least in part, for the reduced Ca2+ transient and force. The prolongation of MAPD and QT interval suggest that Phe could also play a role in the inhibition of repolarizing K+ currents which was confirmed by a significant 70 % reduction (Control – 3.3 ± 0.4 pA/pF; Phe – 1.0 ± 0.3 pA/pF; p < 0.01; unpaired t-test) in the delayed rectifier K+ current (IKr) following 10 µM Phe exposure. Using a dose-response curve the IC50 for Phe on IKr was 7.2 ± 0.7 µM. Together our data indicate that Phe is cardiotoxic to freshwater salmonids and operates via similar mechanisms to those identified for marine teleosts.