Doppler indices of transmitral flow are commonly used to assess noninvasively left ventricular (LV) diastolic function in species larger than mice. The objective of our study was to characterize patterns of LV diastolic function in 2 genetically altered mouse models using Doppler- and color M-mode echocardiography. Phospholamban (PLB) reversibly inhibits the sarcoplasmic reticulum Ca(2+) ATPase (SERCA) and is a key regulator of myocardial relaxation. Twelve-week-old PLB knockout mice (PLB/KO) were examined in parallel with age-matched transgenic mice expressing a mutant form of PLB (PLB/N27A) that exhibited superinhibition of SERCA. Transmitral Doppler flow indexes, including isovolumic relaxation time, the ratio of peak early-to-late filling velocities, and deceleration time of peak early transmitral velocity indicate impaired diastolic filling in the PLB/N27A mutants, but improved LV diastolic function in the PLB/KO mice. In addition, a relatively load-independent parameter of LV relaxation measured by color M-mode Doppler, the propagation velocity of early flow into the LV cavity confirmed the observed differences. We conclude that transmitral filling patterns and color M-mode flow propagation velocity reflect changes in myocardial relaxation in mice with genetically altered levels of PLB and may be useful tools to characterize LV diastolic function in other mouse models of disease.