The fracture response of concrete under low-cycle variable amplitude loading at frequencies up to 10 Hz was investigated. The applied loading history, selected to reflect earthquake loads on concrete dams, consisted of a basic sinusoidal oscillation interrupted by occasional spikes. Test results of specimens with different sizes and loading histories are reported. It was determined that the induced damage is both size and loading history-dependent; further, it was found that spikes in the loading history are likely to accelerate crack growth. On the basis of the experimental results, a fracture mechanics-based empirical law for crack propagation under variable amplitude cyclic loading is proposed.